alter ego

UK: /ˌæltərˈiːgəʊ/ US: (ôl′tər ē′gō, eg′ō, al′-)

WordReference Random House Learner's Dictionary of American English © 2026

ˈal•ter ˈe•go, n. [countable]

1. an inseparable friend.
2. a substitute;
   counterpart.
3. the opposite side of one's personality.

See -alte-.

WordReference Random House Unabridged Dictionary of American English © 2026

al•ter e•go  (ôl′tər ē′gō, eg′ō, al′-), 

1. a second self;
   a perfect substitute or deputy:
   His adviser acts as his alter ego during his absence.
2. an inseparable friend.
3. another aspect of one's self.

• Latin (Cicero), probably translation of Greek állos egó̄, héteros egó̄ another I
• 1530–40

Collins Concise English Dictionary © HarperCollins Publishers::

alter ego / ˈæltər ˈiːɡəʊ ˈɛɡəʊ/ noun

1. a second self
2. a very close and intimate friend

Etymology: Latin: other self