隙 - crevice, fissure, discord

gap; opening; room; space

gap; opening; aperture; crevice; crack; chink; space

niche market

to wait for an opportune moment; to bide one's time; to see one's chance

spare moment; free time; interval; break

porosity

one must constantly be on one's guard with ...; one cannot be too careful of ...

chink in the armor (armour)

gap; opening; space

vacant space; aperture; gap; opening

peeping

gap; opening; crevice; crack