や否や（やいなや）
“The moment … / As soon as …” → Used to express that Action B happens immediately after Action A, with no time gap at all, often emphasizing suddenness or immediacy.
N1
Meaning
“The moment … / As soon as …” → Used to express that Action B happens immediately after Action A, with no time gap at all, often emphasizing suddenness or immediacy.
Formation
Verb (dictionary form) + や否や
Explanation
や否や（やいなや） is a highly formal literary expression used to describe situations where:
Action A occurs
Instantly, Action B follows
There is no pause, no intention, no delay
It is stronger and more rigid than:
～とたんに
～なり
This grammar is mainly found in:
novels
news-style narratives
historical or descriptive writing
JLPT N1 reading passages
It sounds unnatural in casual conversation.
💡 Core nuance:
“At the very instant X occurred, Y followed.”