踩空

踩空	cǎi kōng	to miss one's step
踩	cǎi	variant of 踩
踩	cǎi	to step on / to tread / to stamp / to press a pedal / to pedal (a bike) / (online) to downvote
空	kōng	empty / air / sky / in vain
空	kòng	to empty / vacant / unoccupied / space / leisure / free time