おもしろくなかった

was not interesting, was not funny

→ 面白い
おもしろ interesting, fun + Adverbial/continuative form of an i-adjective + なかっ Negative past + Past tense
adjective · past Rare #30,866
was not interesting, was not funny
JA: その映画はおもしろくなかった。
EN: That movie was not interesting.
Forms of 面白い

その仕事はあまりおもしろくなかった他方報酬良かった

The job wasn’t very interesting, but on the other hand, it paid well.

彼にはこの単調家庭生活おもしろくなかった

He found this monotonous domestic life uninteresting.

その映画は原作ほどおもしろくなかった

The movie wasn't as interesting as the original book.

実をいうとあの映画は私にはあまりおもしろくなかった

To tell the truth, I didn't find that movie very interesting.

試合はとてもおもしろくなかった

The game was not very interesting.

ゲームはどれもおもしろくなかった

None of the games were interesting.