na-adjective, noun which may take the genitive case particle 'no', noun
Describes a constitutionally weak body or health; often used in medical or formal descriptions of physical frailty. Can also refer to mental or moral weakness in literary contexts.
He has a weak constitution and often catches colds.
A special class was set up for frail children.
He was a frail child.
To strengthen a frail body through exercise.
To improve a frail constitution through dietary therapy.
弱い is a general i-adjective for weakness in any sense (body, mind, taste, etc.), while 虚弱 is a more formal term specifically for constitutional physical frailty.
脆弱 describes something fragile or vulnerable (often structures, systems, or defenses), whereas 虚弱 is used specifically for a person's frail physical constitution.
虚弱 typically describes a person's frail physical constitution, while 弱体 can describe either a person's weak body or a weak organization/system.
丈夫 means sturdy or healthy, the opposite of 虚弱's meaning of being physically frail.
頑健 describes someone as robust and physically tough, contrasting with 虚弱's sense of frailty.
虚弱 describes a weak, frail constitution, the direct opposite of the robust, sturdy build described by 強壮.
Compound of 虚 (kyo, 'empty, void') and 弱 (jaku, 'weak'). The combination conveys a state of inherent weakness or deficiency in physical constitution.