Operation of some household gadgets (3)
I believe the answer is:
use
'operation' is the definition.
(I know that use is a type of activity)
'some household gadgets' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'USE' is hidden in the letters of 'household gadgets'.
'of' acts as a link.
(Other definitions for use that I've seen before include "Employ (something)" , "exercise" , "particular church liturgy" , "Operate" , "Employ - custom" .)