method of least squares has 1 distinct synonym spread across 1 of its 1 sense. 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.
a method of fitting a curve to data points so as to minimize the sum of the squares of the distances of the points from the curve
Synonyms, antonyms and the broader and narrower relations for method of least squares come from Princeton University’s WordNet. Full sources and licences.