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Other words with descendants of the root prŏb-
In addition to the cognate verbs Eng. prove ~ Sp. probar and the cognate nouns Eng. proof and probe on one hand and Sp. prueba on the other, there are a number of words in English and Spanish that descend from Latin words that contained the same Latin root prŏb‑ that is at the heart of all these words, a root that is spelled prov‑ in English and prob‑ in (Modern) Spanish. Most of these words have a cognate in the other language, though not all of them do.
Note that not all words that have what looks like the root prov‑ in English come from this source. Most notably, Eng. improve (= Sp. mejorar), which looks like it should be related to the verb prove, is not related to (cognate with) this word at all since it does not descent from a word containing the root prŏb‑. Rather, it comes from Anglo-Norman emprouwer (among other spellings) that meant (among other things) ‘to make a profit’. This verb is related to medieval Latin inpruare or empruare found in British sources in the 12-14th centuries with meanings such as ‘to enrich oneself’, ‘to make a profit’, etc. (OED). There is also a homonym of the verb approve in English that is unrelated to Lat. prŏbāre that used to be a variant of Eng. improve, as we shall see.
There weren’t many Latin words that contained the root prŏb‑ besides (1) the adjective prŏbus/a, the verb prŏbāre ‘to approve, test, etc.’ (source of Sp. probar and Eng. prove), and the noun prŏba ‘proof; test, trial’, source of Sp. prueba and Eng. proof and probe. Remember that the verb was derived from the adjective and the noun from the verb.
- adjective prŏbus/a ‘good, proper, serviceable, excellent, superior, able’, ‘well-behaved, well-conducted’, cf. Sp. probo/a
- verb prŏbāre ‘to try, test, examine, inspect, judge’, ‘to esteem as good, serviceable, fit, just, etc.; to be satisfied with, to approve’, ‘to represent or show a thing to be good, serviceable, fit, right, etc., to make acceptable, to recommend’, ‘to make a thing credible, to show, prove, demonstrate’; cf. Sp. probar, Eng. prove
- noun prŏba ‘a proof’, ‘a test, trial’; cf. Sp. prueba, Eng. proof, probe
- adjective ĭmprŏbus/a (antonym of prŏbus/a) ‘of bad quality, bad, poor, inferior (rare; “mostly post-Aug.)’, enormous, monstrous, excessive’, etc. (L&S); cf. Sp. ímprobo, Eng. (obsolete) improbe
- adverb prŏbē ‘rightly, well, properly, correctly, fitly, etc.’ (CTL)
- Late Latin adjective rĕprŏbus/a ‘false, spurious’ (L&S), formed with the prefix rĕ‑ ‘back, again, against, intensive’; cf. Sp. réprobo/a, Eng. reprobate
- adverb prŏbĭter (pre-classical) ‘well, fitly, capitally (ante-classical)’, ‘well, fitly, thoroughly, very, very much, greatly, finely, capitally, bravely’ (L&S)
- adprŏbāre or apprŏbāre: formed with ad‑ ‘to’; meaning: ‘to assent to as good, to regard as good, to approve, to favor’ (L&S); cf. Sp. aprobar, Eng. approve
- imprŏbāre: formed with the negative prefix in‑ ‘not’ as the antonym of apprŏbāre; meaning: ‘to disapprove, blame, condemn, reject’ (L&S); cf. Sp. improbar, Eng. (obs.) improbate
- rĕprŏbāre: formed in Late Latin with the prefix rĕ‑ ‘back; again’ and used as a synonym of imprŏbāre, the opposite of apprŏbāre; meaning: ‘to disapprove, reject, condemn’ (L&S); cf. Sp. reprobar, Eng. reprove and reprobate, and Fr. réprouver
- comprŏbāre: formed with the prefix con‑ ‘with, together, completely’; meaning: ‘to approve wholly of something, to assent to, sanction, acknowledge’ (L&S); cf. Sp. comprobar, Eng. (obsolete) comprobate
- noun prŏbātĭo ‘a trying, proving’, ‘a trial, inspection, examination’; ‘Approbation, approval, assent’, ‘Proof, demonstration (post-Aug.)’; cf. Sp. (rare) probación, Eng. probation
- noun prŏbātor ‘an approver (rare but classical)’; ‘a trier, examiner (ecclesiastical Latin)’
- noun prŏbātōrĭa ‘a letter of recommendation (from the emperor), a certificate of qualification (postclass.)’
- adjective probātus, converted from the identical passive participle, ‘approved, acceptable, pleasing, agreeable’, ‘tried, tested, proved, approved, good, excellent’; cf. German probat ‘appropriate; suitable; proven’
- adjective prŏbābĭlis ‘that may be assumed, believed, or proved; likely, credible, probable’ and ‘worthy of approval, pleasing, agreeable, acceptable, commendable, laudable, good, fit’; cf. Eng. probable, Sp. probable, Fr. probable
- adjective imprŏbābĭlis, antonym of prŏbābĭlis, formed with the negative prefix in‑, which meant ‘not deserving of approbation, objectionable, exceptionable’ (L&S); cf. Sp. improbable ‘unlikely, improbable’, Eng. improbable
- noun prŏbābĭlĭtas ‘probability, credibility (classical)’; Sp. probabilidad, Eng. probability
- adverb prŏbābĭlĭter ‘probably, credibly’
Go to Part 8
 The verb improve is first attested in English in the late 15th century with the meaning ‘to increase (one’s income); to spend or invest (money) so as to make a profit; esp. to lend at interest’ (OED), a meaning that is now obsolete. It came from and Anglo-French word variously spelled as emprover, emprower, empruer, enprower, enprouwer, or enpruer and meaning ‘to make good use of (a thing) (end of the 13th cent. or earlier), to enclose and cultivate (wasteland or unoccupied land) in order to make it profitable (end of the 13th cent. or earlier), to make profits, to enrich (oneself) (c1300 or earlier, reflexive), to better one’s position (early 14th cent. or earlier, reflexive)’ (OED). This verb is first attested in English in the late 13th century. This verb was formed with the prefix en‑ and the noun prou ‘profit’, descended from Vulgar Lat. prode ‘advantageous, profitable’. In the 17th century, the spelling was fixed as the current one, spelled with a ‑v‑, and not a ‑w‑ as one would have expected, and the pronunciation followed that spelling (OED). The transitive ‘make better’ meaning is from the early 17th century and the intransitive one, ‘get better’, from the first part of the 18th century.
Also unrelated to Lat. aprŏbāre are, of course, the words derived from Eng. improve, namely the adjective improvable (Sp. mejorable) and the noun improvement (Sp. mejora).