frank has 16 distinct synonyms spread across 3 of its 6 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 member of the ancient Germanic peoples who spread from the Rhine into the Roman Empire in the 4th century
a smooth-textured sausage of minced beef or pork usually smoked; often served on a bread roll
exempt by means of an official pass or letter, as from customs or other checks
characterized by directness in manner or speech; without subtlety or evasion
“blunt talking and straight shooting”
1 of the 6 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for frank.
Synonyms, antonyms and the broader and narrower relations for frank come from Princeton University’s WordNet. Full sources and licences.