tridentPronunciation: /ˈtrʌɪd(ə)nt/Definition of trident noun 1a three-pronged spear, especially as an attribute of Poseidon (Neptune) or Britannia. 2 (Trident) a US design of submarine-launched long-range ballistic missile. Origin: late Middle English: from Latin trident-, from tri- 'three' + dens, dent- 'tooth'trident in other Oxford dictionaries Definition of trident in the US English dictionary