less
adj.adj. a smaller amount of something. You use it when you are talking about things you cannot count, like water, time, or money.
adj. a smaller quantity or degree of something. Best for amounts you cannot count, like water, time, or money; for individual items, prefer 'fewer'.
I try to spend less money on coffee.
The new engine design uses significantly less fuel while providing the same amount of power.
The architect argued that using less ornamentation would actually enhance the building's structural beauty, following the famous principle that less is more.
Adverb From Middle English les, lesse, leasse, lasse, from Old English lǣs (“smaller, less”), from Proto-Germanic laisiz, from Proto-Indo-European leys- (“to shrink, grow thin, be gentle”). Cognate with Old Frisian lēs (“less”), Old Saxon lēs (“less”). According to Kroonen (2013), from a northern Indo-European root Proto-Indo-European leh₂is- or leh₃is-, which he connects to Lithuanian liesas (“lean”). Determiner and preposition from Middle English lees, lesse, leasse, lasse, from Old English lǣssa (“less”), from Proto-Germanic laisizan-, from Proto-Germanic laisiz (“smaller, lesser, fewer, lower”) (see above). Cognate with Old Frisian lessa (“less”). Verb from Middle English lessen, from the determiner. Noun from Middle English lesse, from the determiner.
From Middle English lesse, les, from Old English lǣs, as in þȳ lǣs þe.
Typically precedes uncountable nouns. In informal speech, it is frequently used with plural countable nouns, though 'fewer' is preferred in formal writing.
I have less books than youI have fewer books than youIn formal English, 'less' is for uncountable amounts, while 'fewer' is for countable items like books.