Radical 穴
8 strokes
hole 穴 (616a) + work 工 (147) = empty 空
空气 (411) kōngqì air
[空间 (345) kōngjiān space, room]
[空中 (33) kōngzhōng in the air]
[太空 (48) tàikōng (outer) space]

Digging the hole (for the elephant trap) had been a lot of work— but day after day it remained empty. / One day the giant sprained his ankle in it, and was so cross that he filled it in with concrete.