Nickel unit (4)

I believe the answer is:
atom
(Other definitions for atom that I've seen before include "Scrap" , "Very small object or amount" , "Tiny particle, great bomb" , "The tiniest particle" , "Small amount of matter" .)
I believe the answer is:
atom
(Other definitions for atom that I've seen before include "Scrap" , "Very small object or amount" , "Tiny particle, great bomb" , "The tiniest particle" , "Small amount of matter" .)