expression
well done; good job
An exclamation praising someone's achievement, similar to 'well done!' or 'good job!'. It is the past tense of the verb 出来す (でかす), meaning 'to accomplish' or 'to pull off'.
See also: 出来す (でかす)
でかした！よくやったね。
Well done! You did a great job.
テストで満点を取ったんだって？でかした！
I heard you got a perfect score on the test? Good job!
出来す is the base verb meaning 'to accomplish' or 'to pull off'; でかした is its past tense form used as an exclamation.
Past tense of the verb 出来す (でかす), meaning 'to accomplish' or 'to manage to do'. The exclamation でかした is a fixed expression praising a completed action.