mid-14c., proposen, "form a design or intention;" late 14c., "put forward or offer for consideration;" from Old French proposer "propose, advance, suggest" (12c.), from pro "forth" (see pro-) + poser "put, place" (see pose (v.1)). The notion is "place before as something to be done." The French word took the place of Latin proponare (for this substitution, see pose (v.1)). The meaning "make an offer of marriage" is attested by 1764. Related: Proposed; proposing. See also propone, which coexisted with this word for a time.
suffix forming nouns of action from verbs, mostly from Latin and French, meaning "act of ______ing" (such as survival, referral), Middle English -aille, from French feminine singular -aille, from Latin -alia, neuter plural of adjective suffix -alis, also used in English as a noun suffix. Nativized in English and used with Germanic verbs (as in bestowal, betrothal).
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Harper, D. (n.d.). Etymology of proposal. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/proposal