foreign has 3 distinct synonyms spread across 3 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 2 recorded opposites are domestic, native.
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.
of concern to or concerning the affairs of other nations (other than your own)
“foreign trade”
not contained in or deriving from the essential nature of something
“an economic theory alien to the spirit of capitalism”
Synonyms, antonyms and the broader and narrower relations for foreign come from Princeton University’s WordNet. Full sources and licences.
not belonging to that in which it is contained; introduced from an outside source
“water free of extraneous matter”