Meaning

adjective giving careful attention to detail; hard to please; excessively concerned with cleanliness

adjective having complicated nutritional requirements; especially growing only in special artificial cultures

originBorrowed from Latin fastīdiōsus (“passive: that feels disgust, disdainful, scornful, fastidious; active: that causes disgust, disgusting, loathsome”), from fastīdium (“a loathing, aversion, disgust, niceness of taste, daintiness, etc.”), perhaps for *fastutidium, from fastus (“disdain, haughtiness, arrogance, disgust”) + taedium (“disgust”). Cf. French fastidieux.

Etymology from Wiktionary, CC BY-SA 3.0