1375-1425;late Middle English < Latinfastīdiōsus squeamish, equivalent to fastīdi(um) lack of appetite, disgust, perhaps by syncope of *fastutīdium (fastu-, combining form of fastus pride, conceit + -tīdium combining form of taediumtedium) + -ōsus-ous
mid-15c., "full of pride," from L. fastidiosus "disdainful, squeamish, exacting," from fastidium "loathing," most likely from *fastu-taidiom, a compound of fastus "contempt, arrogance" and tædium "aversion, disgust." Early use in Eng. was in both passive and active senses. Meaning "squeamish, over-nice" emerged in English 1610s. Related: Fastidiously; fastidiousness.