shadow has 16 distinct synonyms spread across 6 of its 12 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.
a premonition of something adverse
“a shadow over his happiness”
an indication that something has been present
“there wasn't a trace of evidence for the claim”
refuge from danger or observation
“he felt secure in his father's shadow”
a dominating and pervasive presence
“he received little recognition working in the shadow of his father”
an inseparable companion
“the poor child was his mother's shadow”
follow, usually without the person's knowledge
“The police are shadowing her”
Synonyms, antonyms and the broader and narrower relations for shadow come from Princeton University’s WordNet. Full sources and licences.
make appear small by comparison
“This year's debt dwarfs that of last year”