adverb
Concessive conjunction used in formal or literary Japanese. Often paired with とも or ても, as in よしんば. The standalone よし is somewhat old-fashioned.
よし失敗しても、後悔はしない。
Even if I fail, I won't regret it.
よしんば彼が来なくても、会議は予定通り行う。
Even if he doesn't come, we'll hold the meeting as scheduled.
たとえ is the standard modern word for 'even if', while よし is literary and less common.
よしんば is a more emphatic or formal version of よし, often used in hypothetical concessions.
Derived from classical Japanese concessive expression. The exact historical derivation is uncertain, but it functions as a conjunction meaning 'even if'.