Learner's definition of ANONYMOUS
1 : not named or identified 2 : made or done by someone unknown
The college received an anonymous gift.
He made an anonymous phone call to the police.
The reporter got an anonymous tip.
3 [more anonymous; most anonymous] : not distinct or noticeable : lacking interesting or unusual characteristics
She works in an anonymous [=bland, nondescript] brick building.
His was just another anonymous face in the crowd.