Forsooth is formed from the combination of the preposition for and the noun sooth. Sooth survives as both a noun (meaning "truth" or "reality") and an adjective (meaning "true," "sweet," or "soft"), though it is rarely used by contemporary speakers.

What does forsooth mean in Shakespearean?

forsooth - an archaic word originally meaning `in truth' but now usually used to express disbelief.

Where did the word lackadaisical originate?

It owes its origin, strangely enough, to an old saying of regret or dismay, lack-a-day!, a shortened form of alack-a-day! Alack dates back to medieval times, and probably comes from a dialect word lack that is variously interpreted as failure, fault, reproach, disgrace, or shame.