hairline

1 being of less than usual width a hairline crack in the mug, almost too small to notice, was enough to make the mug break when filled with hot tea Synonyms fine, narrow, needlelike, paper-thin, skinny, slender, slim, slim-jim, thin, ultrathinRelated Words attenuate, attenuated, elongate (or elongated), linear; bottleneck, close, compressed, condensed, constricted, contracted, squeezed, tight, tightened; lanky, rangy, reedy, shoestring, spindly, stalky, stringy, twiggy, willowy, wispy; lank, spareNear Antonyms chunky, squat, stocky, stumpy, thick, thickset; bulky, massive, voluminous; thickish, widishAntonyms broad, fat, wide

2 made or done with extreme care and accuracy a hairline distinction between her rating of certain things as “necessary” and others as “absolutely necessary” Synonyms delicate, exact, finespun, fine, hairsplitting, minute, nice, nuanced, refined, subtleRelated Words nitpicking, quibbling; frivolous, inconsequential, inconsiderable, insignificant, negligible, petty, piddling, trifling, trivial; demanding, exacting, fastidious, finical, finicking, finicky, fussy, meticulous, particular, pickyNear Antonyms apparent, clear, clear-cut, evident, manifest, obvious, open-and-shut, palpable, patent, perspicuous, plain, transparent, unambiguous, unequivocal, unmistakable; broad, indefinite; careless, heedless, incautious, slapdash, slipshod, sloppyAntonyms coarse, inexact, rough

3 meeting the highest standard of accuracy an ultrasensitive telescope that requires hairline placement of the lenses Synonyms accurate, close, delicate, exact, fine, precise, mathematical, pinpoint, refined, rigorous, spot-onRelated Words correct, right, strict, true; definite, definitive; nice, subtle; careful, fastidious, finical, finicky, meticulousNear Antonyms approximate, round; false, incorrect, untrue, wrong; careless, loose; indefinite, unclear, vague; doubtful, dubious, questionable, unreliable, untrustworthyAntonyms coarse, imprecise, inaccurate, inexact, rough