Possibly means perhaps — it could be so, and it could not. Possibly tomorrow, possibly not, that is possibly the best of them.
As a hedge it is slightly weaker than probably and about level with perhaps and maybe. It has a second, quite different job: with can and could it means at all, marking the limit of what is achievable — I cannot possibly finish today, do everything you possibly can. And in requests, could you possibly is one of the politest forms English has, precisely because it pretends to doubt whether the thing is even possible.
1adverbpossiblyPerhaps; it could be so.
“Possibly the best decision they made all year.”
synonyms: perhaps, maybe, conceivably
2adverbemphasisAt all, used with can or could for emphasis.
“I cannot possibly get there before six.”
Too few real examples of this word to estimate which sense is commonest.
possibly is a degree of likelihood.
Proto-Indo-European
*h₁es-
Latin
possibilis — possible
Old French
possible
Middle English
possible
English
possible
English, today
possibly
Built from
From possible + -ly. possible comes from Middle English possible, from Old French possible, from Latin possibilis (“possible”), from possum (“to be able”); see power. Displaced acumendlic, from ācumendlīċ. Compare also mihtelīċ, which was cognate with mahtlīh and máttulígr. Compare also mogelijk and möglich.
Etymology from Wiktionary, CC BY-SA