House used by commanding officer, teetotal, ahead of time (7)
I believe the answer is:
cottage
'house' is the definition.
(I know that cottage is a type of house)
'commanding officer teetotal ahead of time' is the wordplay.
'commanding officer' becomes 'co'.
'teetotal' becomes 'tt' (abbreviation).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'time' becomes 'age' (an age is a period of time).
'co'+'tt'+'age'='COTTAGE'
'used by' is the link.
(Other definitions for cottage that I've seen before include "Small living space" , "Rural dwelling" , "Small house, in the country say" , "Small single-storey dwelling" , "Small home" .)