na-adjective
instructive; didactic
Describes something that teaches a lesson or moral, often with a slightly formal or literary tone.
この話はとても教訓的だ。
This story is very instructive.
彼のスピーチは教訓的な内容だった。
His speech had a didactic content.
教訓 (lesson, moral) + 的 (-like, -ish). The derivation is straightforward; the exact historical origin of 教訓 is uncertain but it is a Sino-Japanese compound.