KanjiJLPT N2
Dull

dull, slow, foolish, blunt

Mnemonic

A gold blade was left forgotten in the barracks for decades. Without anyone to sharpen or polish it, the once-brilliant edge grew dull—so dull that new recruits mistook it for a butter knife and spread jam with it every morning.
Additional thoughts
Picture a gleaming gold sword propped in a dusty barracks corner, slowly tarnishing and losing its edge over the years until it's embarrassingly dull.
Quick recall
A gold blade abandoned in the barracks slowly becomes dull.

Details

The keyword for 鈍 is dull. This kanji refers to a lack of sharpness, whether in a physical or metaphorical sense. It can describe a blade that has lost its edge, a mind that is slow to comprehend, or senses that are not acute. More broadly, it conveys the idea of sluggishness, obtuseness, or a general lack of keenness in response or perception.
On'yomi
どん
Kun'yomi
にぶ.い、にぶ.る、にぶ-、なま.る、なまく.ら