Lacking strength or solidity; feeble or weak (in ability, evidence, will, etc.). Often used in written or formal contexts.
その主張は証拠が薄弱で、説得力に欠ける。
That claim is weak on evidence and lacks persuasiveness.
最近のチームは精神的に薄弱で、ちょっとしたミスですぐ動揺する。
The team has been mentally weak lately and gets unsettled by small mistakes.
薄弱な体力では山登りは難しい。
With weak physical strength, mountain climbing is difficult.