否定表現N4
〜ず（に）
without doing...
Structure
V-ない形（語幹）+ ず（に）
Explanation
ず is a literary negative auxiliary, equivalent to ない. Attached to the nai-stem of verbs, 〜ず（に）expresses doing the latter action without doing the former, similar to 〜ないで. Common in writing and formal speech; 〜ないで is more common in conversation. Note that the negative of する is せず.
Examples
朝ご飯を食べずに学校へ行きました。
I went to school without eating breakfast.
辞書を使わずに日本語の新聞を読みます。
I read Japanese newspapers without using a dictionary.
Note
The negative of する is せず: e.g. 勉強せずに遊ぶ. In speech, 〜ないで is more common; 〜ず（に）sounds formal and literary.
Related Grammar
〜ないで〜ない