Fastidious
Etymology
From Latin fastidium, "loathing, squeamishness, disgust," probably a blend of fastus, "arrogance, disdain," and taedium, "weariness." It entered English meaning disgusted or squeamish, and that squeamishness evolved into today’s sense of scrupulous, exacting attention to detail. The old note of distaste survives faintly: the fastidious person is one who is easily put off by anything not up to standard.
adjective · /fa-STID-ee-us/
Very attentive to detail and hard to please, often to the point of fussiness.
What it names
A demanding exactness about cleanliness, accuracy, or standards — care so meticulous it shades into being difficult to satisfy.
Example
She was fastidious about her sources, chasing down the original document rather than trusting a summary.
Related idea
Meticulous is simply painstaking about detail; fastidious adds fussiness and a hint of squeamish, hard-to-please distaste.