Computer — coat (3)
I believe the answer is:
mac
This clue is a double definition.
'computer' is the first definition.
(I know that Mac is a type of personal computer)
'coat' is the second definition.
(I know that mac is a type of raincoat)
(Other definitions for mac that I've seen before include "It may help you keep dry" , "one used in shower?" , "laptop?" , "Coat - computer" , "Waterproof coat (colloq.)" .)