acrobatics; risky undertaking
Literally acrobatics or a stunt; figuratively a risky or daring venture. The figurative use is common in business and personal contexts.
I saw acrobatics at the circus.
そんな計画は軽業だ。
That plan is a risky undertaking.
acrobat
Compound of 軽 (かる, light, nimble) and 業 (わざ, act, deed). The reading わざ for 業 is a native Japanese word meaning 'act' or 'technique'.