To become blunt or lose sharpness (literally, e.g., a blade's edge becoming dull).
包丁の切れ味が鈍ってきたので研いだ。
The kitchen knife had gone dull, so I sharpened it.
何度も使ううちにナイフが鈍る。
With repeated use the knife becomes dull.
鉛筆の先が鈍っているから削ってください。
The pencil tip is blunt, so please sharpen it.
To become less capable, to weaken, or to dull (of senses, skills, reactions, judgment).
練習をさぼると勘が鈍る。
If you skip practice, your instincts will dull.
年を取ると反応が鈍ることがある。
As people age, their reactions can become slower.
景気が悪くて消費意欲が鈍っている。
Economic weakness has dampened consumer spending desire.