Perchance means perhaps, in old or poetic use. Perchance to dream, perchance you know, if perchance.
It survives almost entirely as archaism and as a joke. To sleep, perchance to dream is from Hamlet and is the phrase that keeps it alive. It is built exactly as perhaps is — by chance rather than by hap — and the two words are the same idea in French and English parts. Note perhaps, which won.
1adverbperchancePerhaps, in old or poetic use.
“If you should perchance see my brother, tell him I'm waiting.”
perchance is an expression of possibility.
Old French par cheance means by chance. Perhaps is the same construction with the English hap, meaning luck, and it displaced perchance entirely.
Old French
par cheance
Middle English
parchaunce
English, today
perchance
From Middle English parchaunce, from Old French par cheance, from par. From Middle English parchaunce, from Old French par cheance (“by chance”).
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire