noun
slight yawn; half-suppressed yawn
A yawn that is not fully open or is stifled, often involuntary or done discreetly.
会議中に生あくびが出てしまった。
I let out a slight yawn during the meeting.
彼女は生あくびをかみ殺した。
She stifled a half-yawn.
あくび is a general yawn, while 生あくび specifically refers to a slight or suppressed yawn.
Compound of 生 (nama, 'raw, half-hearted') and あくび (akubi, 'yawn'). The prefix 生 adds a nuance of something incomplete or not fully realized.