本质

nature; spirit; essence; substance; quiddity; intrinsic nature; innate character; inherent; intrinsic; essential; in essence; in nature; at heart

虚弱

weak; frail; feeble; debilitated; infirm; delicate; faint; fragile; sickly; woozy; weakly; weakness; frailty; debility; infirmity; weaken; debilitate