noun, noun which may take the genitive case particle 'no'
Used to describe something happening for the first time or being the initial instance. Often appears in formal or technical contexts.
This was decided at the first meeting.
I passed the initial screening.
Compound of 一次 (first, primary) and 回 (time, occasion). The exact derivation is uncertain, but it follows a standard pattern for forming nouns indicating an initial occurrence.