등단이 · 등단을
literary debut, debut as a writer
Example
그녀는 신춘문예에 당선되어 시인으로 등단했어요.
She won the New Year's literary contest and debuted as a poet.
Word parts
등 ascend+단 platform
Literally 'ascending the platform' — stepping onto the literary stage.
Good to know
Usually used as 등단하다; 'X(으)로 등단하다' means to debut as X, e.g. 시인으로, 소설가로.