Slightly means a little bit — enough to notice, not enough to matter much. A picture hanging slightly crooked, a shirt slightly too big across the shoulders, bathwater that has gone slightly cold.
It sits in front of the word it softens: slightly late, slightly annoyed, slightly better. With comparatives it is one of the safest tools English has for taking the edge off a claim — slightly cheaper, slightly more difficult, slightly worse than last year. It does not go with absolutes, so nothing is slightly enormous and nobody is slightly dead. Two relatives worth keeping straight: the adjective slight means small or thin, but a slight as a noun is an insult, and to slight someone is to snub them. 'Not in the slightest' means not at all.
1adverbslightlyTo a small degree; a little.
“The door was slightly open and the hall light was showing.”
synonyms: a little, somewhat
2adverbcomparativeUsed before a comparative to mark a small difference.
“This route is slightly shorter than the one along the river.”
Too few real examples of this word to estimate which sense is commonest.
Proto-Germanic
*slihtaz — slippery, flat, level, plain
Old English
sliht — smooth, level
Middle English
slight — bad, of poor quality, unimportant, trivial, slender, slim, smooth, level
English
slight
English, today
slightly
From slight + -ly. slight comes from Middle English slight (“bad, of poor quality, unimportant, trivial, slender, slim, smooth, level”), from Old English sliht (“smooth, level”), from Proto-Germanic slihtaz (“slippery, flat, level, plain”), related to English slick. Cognate with Scots slicht (“bad, of poor quality”), West Frisian sljocht (“smooth, level, plain, simple”), Dutch slecht (“bad”), Low German slecht (“bad”), German schlecht (“bad”) and schlicht (“plain, artless, natural”), Danish slet (“bad, evil, poor, nasty, wrong”), Swedish slät (“smooth”), Norwegian Bokmål and Norwegian Nynorsk slett (“even”), Icelandic sléttur (“even, smooth, level”).
Etymology from Wiktionary, CC BY-SA