無くす
なくす · nakusu · JLPT N5 · verb-godan
to lose something
🔑 無 (nothing) + くす: to make it nothing = lose it
無 means none or nonexistent, as in 無い (nai, there is none). 無くす is the transitive partner: you cause a thing to become none. Its pair 無くなる (nakunaru) means the thing goes missing by itself.