By attaching the prefix dĭs‑, to the verb sĕdēre, the derived verb dĭssĭdēre was formed in Latin. (Note that here too the derived verb has the sĭd‑ allomorph of the sĕd‑ morpheme.) The prefix’s meaning in this context was ‘asunder, apart, in two’ (other meanings of the prefix dĭs‑ are ‘reversal, removal’ and ‘utterly, exceedingly’ (intensifier). Thus, the main meaning of the verb dĭssĭdēre was ‘to sit apart’ and, derived from it, ‘to be remote from, to be divided, separated’ (L&S). A secondary, derived, figurative meaning was ‘to be at variance, disagree, differ’ (CTL). The verb’s principal parts were (present indicative) dĭssĭdĕō, (present infinitive) dĭssĭdēre, and (perfect active) dĭssēdī (this verb had no supine or passive participle forms).
The verb itself was not passed on to either French or Spanish patrimonially but the present participle of this verb appears around the same time in the 16th century in both French and English. Remember that the present participle of a Latin verb was an adjective and it was formed with the ‑nt‑ suffix (‑ns in the nominative; cf. Part I, Chapter 8, §18.104.22.168.3.3). The nominative form of this verb’s participle was dĭssĭdēns and the accusative wordform was dĭssĭdĕntem (regular stem: dĭssĭdĕnt‑, morphemes: dĭs‑sĭd‑ĕ‑nt). From this word come the loanwords Eng. dissident [ˈdɪ.sɪ.dənt] and Fr. dissident [di.si.ˈdɑ̃] (fem. dissidente [di.si.ˈdɑ̃t]). The word was little used until the 18th century, however, when political dissidence started to be a bigger problem for governments.
The word dissident can be used as an adjective and, particularly, as a noun. Its adjectival meaning is ‘in opposition to official policy’ and as a noun it means ‘a person who opposes official policy’ (COED). Common collocations of the adjectival use in English are dissident opinion and dissident writer and of the noun use political dissident and religious dissident.
Some dictionaries have more narrow definitions and assume that dissidents disagree only with governments and that dissidents only exist in certain countries. Thus, one such dictionary defines dissident as ‘someone who publicly criticizes the government in a country where this is punished’ (DOCE). This is obviously too narrow a definition, for one may also be a dissident inside an organization, such as a political party or an organized religion, for example. And, there are also dissidents in countries where disagreeing with the government is not particularly dangerous. Such dissidents are typically ignored as long as the government doesn’t see their dissidence as dangerous.
Spanish has also borrowed this word and the cognate of Eng. dissident is Sp. disidente, which is also both an adjective and a noun, with the same meaning as its English counterpart. This word is not attested until the early 19th century in Spanish and, thus, there is no doubt that it came into the language through French or English.
Interestingly, Spanish also borrowed the verb disidir from Lat. dĭssĭdēre around the same time. This verb has the meaning ‘to separate oneself from the common doctrine, belief, or behavior’ (DLE). The verb has been rarely used since around 1850, however. It is not clear why when this verb was borrowed from Latin, it was borrowed as a third conjugation verb and not as a second conjugation one.
In addition to this noun/adjective, each of these three languages has an abstract noun derived from it, cf. Eng. dissidence ~ Sp. disidencia ~ Fr. dissidence, all meaning ‘disagreement, as of opinion or belief’ (AHD). The Latin word that these three words descend from is dĭssĭdĕntĭa, a word that did not exist in Latin and is thus a New Latin creation that was formed in a regular manner from the participle stem dĭssĭdĕnt‑ by the addition of the suffix ‑ĭ‑a that formed abstract nouns, usually from adjective stems (remember that the present participle is an adjective in Latin).
Patrimonial and early borrowings from Latin words that had the ‑nt‑ĭa ending had resulted in French words in ‑nce and Spanish words in ‑ncia (Lat. ‑a‑nt‑ĭa from first conjugation verbs changed to ‑ance and ‑ancia, respectively, and Lat. ‑e‑nt‑ĭa from other conjugations changed to ‑ence and ‑encia respectively). The ‑nce ending of French words was borrowed into English early on, which explains why the French and the English cognates have identical form. Thus, when the time came to derive an abstract noun from Eng. dissident and Sp. disidente, the only option was to come up with Eng. dissidence and Sp. disidencia.
Excursus: Lat. dĭssĕntīre
A partial synonym of the English noun dissidence is dissent, which is both a noun and a verb. The verb to dissent (from), which came first, means ‘express disagreement with a prevailing view or official decision’ (COED) and the noun dissent, which is derived by conversion (zero-derivation) from the verb, means ‘the holding or expression of a dissenting view’ (COED). However, the words dissidence and dissent are not related to each other except that in both cases the Latin source word contains the same prefix dĭs‑.
The verb dissent was borrowed in the early 15th century from the Latin verb dĭssĕntīre ‘to differ, dissent, disagree, be at odds, contradict, quarrel’ derived from sĕntīre ‘to feel, perceive with the senses; to have an opinion; to feel an emotion’, source of Sp. sentir and Eng. sense (dĭs‑sĕnt‑ī‑re; principal parts: dĭssĕntĭō, dĭssĕntīre, dĭssēnsī, dĭssēnsum). (The English verb to sense is a cognate, since it is derived from the passive participle form sēnsus as opposed to from the infinitive like its Spanish counterpart.)
Spanish too borrowed the Latin verb dĭssĕntīre, as disentir. This verb is conjugated like sentir and was first attested in the early 17th century. Its meaning is ‘not to share someone else’s feeling or opinion’ and it is closer to the English verb disagree, though it can also be equivalent to dissent. It is used in sentences such as Disiento de tu opinión ‘I disagree with your opinion’. Both Eng. dissent and Sp. disentir are intransitive verbs, but they are not used identically. Basic to the notion of Eng. dissent is the expression of disagreement, whereas disentir in Spanish is just about having the disagreement, without necessarily expressing it.
Spanish has three nouns derived from this verb namely disentimiento, disenso, and disensión. They are all quite rare and neither one is necessarily equivalent to the English noun dissent. Sp. disensión is first attested in the late 15th century, even earlier than the verb disentir, and it is a loanword from the Latin word dĭssēnsĭo (regular stem: dĭssēnsĭōn‑), which meant ‘difference of opinion, disagreement, dissension, discord’ and was derived from the passive participle stem dĭssēns‑ and the abstract noun forming suffix ‑ĭōn‑. English has a cognate dissension [dɪ.'sɛn.ʃən] that means ‘disagreement that leads to discord’ (COED). These cognates are not the best of friends, however. In Sp. disensión the idea of ‘discord’ is not as strong as in Eng. dissension and thus it often translates best as disagreement (Sp. desacuerdo), whereas Eng. dissension often translates best as discordia (Eng. discord).
Sp. disenso and disentimiento are synonyms that mean ‘action or result of disentir’ (DLE). Sp. disenso is a loanword from Lat. dĭssēnsus, a Latin noun converted from the (identical) masculine passive participle of the verb dĭssĕntīre that meant ‘dissension, disagreement, discord’ (L&S). The noun disentimiento, probably the rarest of the three nouns, was derived, in Spanish, from the verb disentir with the noun-forming suffix ‑miento.