k has 25 distinct synonyms spread across 7 of its 8 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the basic unit of thermodynamic temperature adopted under the Systeme International d'Unites
a light soft silver-white metallic element of the alkali metal group; oxidizes rapidly in air and reacts violently with water; is abundant in nature in combined forms occurring in sea water and in carnallite and kainite and sylvite
the cardinal number that is the product of 10 and 100
the 11th letter of the Roman alphabet
street names for ketamine
denoting a quantity consisting of 1,000 items or units
Synonyms, antonyms and the broader and narrower relations for k come from Princeton University’s WordNet. Full sources and licences.