noun which may take the genitive case particle 'no', noun
a mere; only a; insignificant
Used before a noun with の to belittle or humble the following noun, often oneself or one's status. Common in set phrases like 一介のサラリーマン (a mere office worker).
私は一介の学生に過ぎません。
I am nothing more than a mere student.
彼は一介の平社員から社長にまで出世した。
He rose from a mere rank-and-file employee to company president.