Úplná (čistá, absolutní) synonyma jsou ta, která mají zcela totožný význam a lze je volně zaměnit ve všech kontextech, kromě ustálených obratů ([[přísloví]], [[pořekadlo|pořekadel]] apod.). Takových synonym je ovšem velice málo. Příklady: ''hezký – pěkný, chlapec – hoch''. Zvláštní kategorií jsou synonyma, která se liší pouze stylovou platností (''táta – tatínek'') a dvojice českého pojmu s přejatým, tzv. '''jazykové ekvivalenty''' (''přeprava – transport'').
Daleko běžnější jsou synonyma neúplná (částečná), jejichž významy jsoujjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjsou navzájem blízké, ale nikoli totožné. Částečná synonyma se liší kontextovým a stylovým užitím, obsahem i rozsahem významu (''červený – rudý''), intenzitou (''práce – dřina''), dobovým užitím (''krmě – jídlo''), frekvencí užití (''málokdy – zřídkavě''). Za synonyma se považují i slova odvozená nebo slovotvorné varianty (''dítě – děcko, jevit – projevit''). Synonymy jsou také výrazy [[nářečí|nářeční]], [[argot]]ické, [[slang]]ové, které doplňují neutrální výraz (''chlapec – ogar''). Naproti tomu varianty tvaroslovné a hláskové se za synonyma nepovažují (''brambor – brambora, vzlítnout – vzlétnout''). Některá sousloví, zejména pořekadla a ustálené obraty, mají někdy svůj slovní synonymní protějšek (''zůstat na ocet – neprovdat se'').
Zvláštním druhem synonym jsou tzv. synonyma '''idiografická''', která se liší ve věcném významu, tudíž označují skutečnost z jiného hlediska (''moudrý - chytrý, smělý - nebojácný''). Tato synonyma můžeme dále rozdělit do dvou podskupin:
