largeness has 6 distinct synonyms spread across 4 of its 4 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. Its one recorded opposite is smallness.
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 capacity to understand a broad range of topics
“a teacher must have a breadth of knowledge of the subject”
large or extensive in breadth or importance or comprehensiveness
“the might have repercussions of unimaginable largeness”
Synonyms, antonyms and the broader and narrower relations for largeness come from Princeton University’s WordNet. Full sources and licences.
the property of having a relatively great size
the quality of being pretentious (behaving or speaking in such a manner as to create a false appearance of great importance or worth)