size has 2 distinct synonyms spread across 2 of its 9 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 physical magnitude of something (how big it is)
“a wolf is about the size of a large dog”
the property resulting from being one of a series of graduated measurements (as of clothing)
1 of the 9 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for size.
Synonyms, antonyms and the broader and narrower relations for size come from Princeton University’s WordNet. Full sources and licences.
“he wears a size 13 shoe”
the actual state of affairs
“that's the size of the situation”
a large magnitude
“he blanched when he saw the size of the bill”
cover or stiffen or glaze a porous material with size or sizing (a glutinous substance)
make to a size; bring to a suitable size