stretch has 15 distinct synonyms spread across 12 of its 20 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 shrink.
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.
occupy a large, elongated area
“The park stretched beneath the train line”
extend one's limbs or muscles, or the entire body
“Stretch your legs!”
extend or stretch out to a greater or the full length
“Unfold the newspaper”
lie down comfortably
“To enjoy the picnic, we stretched out on the grass”
extend the scope or meaning of; often unduly
“Stretch the limits”
corrupt, debase, or make impure by adding a foreign or inferior substance; often by replacing valuable ingredients with inferior ones
“adulterate liquor”
extend one's body or limbs
“Let's stretch for a minute--we've been sitting here for over 3 hours”
a straightaway section of a racetrack
exercise designed to extend the limbs and muscles to their full extent
extension to or beyond the ordinary limit
“running at full stretch”
2 of the 20 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for stretch.
Synonyms, antonyms and the broader and narrower relations for stretch come from Princeton University’s WordNet. Full sources and licences.