Meaning

verb be agreeable or acceptable to

adjective meeting adequate standards for a purpose

noun a display of bad temper

originPossibly from Middle English fit (“an adversary of equal power”), of uncertain further origin. The original sense appears to have been "to marshal or deploy troops", which shifted to "to suit (troops to a certain location" > "suitable", and may be further related to Icelandic fitja (“to web, knit, cast on”).

Etymology from Wiktionary, CC BY-SA 3.0