noun, na-adjective
commonplace and stale; humdrum and hackneyed
Describes ideas, expressions, or things that are both ordinary and trite, lacking freshness or originality. Often used in critical or literary contexts.
彼のスピーチは平凡陳腐で、誰も感動しなかった。
His speech was commonplace and stale, and no one was moved.
その映画の筋書きは平凡陳腐で、すぐに飽きてしまった。
The movie's plot was humdrum and hackneyed, and I quickly got bored.
A compound of 平凡 (commonplace) and 陳腐 (stale, hackneyed). The exact historical derivation is uncertain, but it is a straightforward combination of two Sino-Japanese words.