godan verb (-ru), intransitive verb
Intransitive: something becomes weaker, less intense, or subsides. Used for wind, rain, force, influence, pain, etc. The glosses 'to be emaciated', 'to be dejected', and 'to be perplexed' are rare, literary, or context-specific extensions; the core meaning is weakening or abating.
台風の勢力が次第に弱まった。
The typhoon's strength gradually weakened.
薬が効いて痛みが弱まった。
The medicine took effect and the pain subsided.