Kanji with the 穴 Radical (cave)

empty, sky, void, vacant, vacuum

kuu

research, study

kyuu

stab, protruding, thrust, pierce, prick, collision, sudden

totsu

window, pane

sou

hole, aperture, slit, cave, den

ketsu

hard up, destitute, suffer, perplexed, cornered

kyuu

plug up, obstruct

chitsu

stealth, steal, secret, private, hushed

setsu

kiln, oven, furnace

you

cavern

kutsu