promnesia (n.)

"loss of memory," 1786 (as a Greek word in English from 1670s), Modern Latin, from Greek amnesia "forgetfulness," from a- "not" (see a- (3)) + mnesi- "remembering" (found only in compounds), from stem of mnasthai "to recall, remember," which is related to mnemnon "mindful," mneme "memory" (from PIE root *men- (1) "to think"). The usual compound in Greek was amnestia, but this had a specialized sense of "forgetfulness of wrong" (see amnesty).

"feeling of having previously experienced a present situation," 1903, from French déjà vu, literally "already seen." The phenomenon also is known as promnesia. Similar phenomena are déjà entendu "already heard" (of music, etc.), 1965; and déjà lu "already read" (1960).

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.