"tallness, loftiness," 1540s, from obsolete French procerité or directly from Latin proceritas, from procerus "high, tall," from pro "before, forth" (see pro-) + -cerus, from stem of crescere "to grow" (from PIE root *ker- (2) "to grow").
word-forming element meaning "forward, forth, toward the front" (as in proclaim, proceed); "beforehand, in advance" (prohibit, provide); "taking care of" (procure); "in place of, on behalf of" (proconsul, pronoun); from Latin pro (adv., prep.) "on behalf of, in place of, before, for, in exchange for, just as," which also was used as a first element in compounds and had a collateral form por-.
Also in some cases from cognate Greek pro "before, in front of, sooner," which also was used in Greek as a prefix (as in problem). Both the Latin and Greek words are from PIE *pro- (source also of Sanskrit pra- "before, forward, forth;" Gothic faura "before," Old English fore "before, for, on account of," fram "forward, from;" Old Irish roar "enough"), extended form of root *per- (1) "forward," hence "in front of, before, toward, near," etc.
The common modern sense of "in favor of, favoring" (pro-independence, pro-fluoridation, pro-Soviet, etc.) was not in classical Latin and is attested in English from early 19c.
It is the hypothetical source of/evidence for its existence is provided by: Greek kouros "boy," korē "girl;" Latin crescere "come forth, spring up, grow, thrive, swell," Ceres, goddess of agriculture, creare "to bring forth, create, produce;" Armenian serem "bring forth," serim "be born."
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Harper, D. (n.d.). Etymology of procerity. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/procerity