Crazy about one domestic (4)
I believe the answer is:
maid
'domestic' is the definition.
(maid is a kind of domestic)
'crazy about one' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'about' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'mad' enclosing 'i' is 'MAID'.
(Other definitions for maid that I've seen before include "Female domestic servant" , "Young woman - servant" , "Serving girl" , "employee" , "Damsel" .)