Lexical changes from Classical Latin to Proto-Romance

As Classical Latin developed into Proto-Romance it gained and lost lexical items for a variety of reasons. Some of the new ones came from contact with neighbouring languages, while others were native coinages. Much of the inherited Latin vocabulary also underwent semantic drift, regularization, or other linguistic changes.
Overview.
Irregular nouns and verbs tended to be either regularized or replaced with prexisting regular equivalents, cf. the loss of "esse" 'to eat' in favour of its own regularized compound "comedere" and also the unrelated "manducare", the latter having originally meant 'chew'. Similar motives underlie the replacement of "ferre" 'carry' with "portare" or "loqui" 'speak' with "parabolare" and "fabulare".
Semantic drift affected numerous words, notable examples of which are "causa" ('subject matter' "→" 'thing'), "civitas" ('citizenry' "→" 'city'), "focus" ('hearth' "→" 'fire'), "mittere" ('send' → 'put'), "necare" ('murder' "→" 'drown'), "pacare" ('placate' "→" 'pay'), and "totus" ('whole' "→" 'all, every').
Words that were felt to be too short or phonetically insubstantial were more likely to be replaced, often with their own derivatives, hence "auris" 'ear' and "agnus" 'lamb' were rejected in favour of the diminutives "auricula" and "agnellus".
A number of verb-forming (or verb-extending) suffixes were popularized, such as -"icare" (based on the adjective ending -"icus"), -"ulare" (based on the diminutive -"ul"-), and -"izare" (a borrowing from Greek).
The majority of borrowed vocabulary came from Greek, particularly in the domains of medicine, cooking, and Christian worship. A lesser fraction came from Gaulish or Germanic.
There was a trend towards forming compound prepositions of the type "ab-ante", which at first simply combined the sense of their two constitutuents (hence the original sense of "abante" was 'from before'). In time many would develop a generic sense, often simply that of one of their constitutents (hence "abante" came to mean 'before', in competition with "ante"). Other examples attested in Late Antiquity are "de-inter", "de-retro", "de-foris", "de-intus", "de-ab", "de-ex", and "de-ab".
Most Classical particles (such as "an, at, autem, donec, enim," etc.) simply died out in popular speech and hence survive nowhere in Romance.