や否や
文法の解説は英語です。
用法
as soon as; the moment ~; the minute (that); no sooner than ~
例文
先生が教室に入るや否や、学生たちはおしゃべりを辞めた
As soon as the teacher entered the classroom, the students stopped talking
友達の赤ん坊が私の顔を見るや否や、泣き出した
As soon as my friend's baby saw my face, it started crying