Army officer in house on short break (9)
I believe the answer is:
semicolon
'short break' is the definition.
(punctuation mark creating a break in a sentence)
'army officer in house on' is the wordplay.
'army officer' becomes 'col' (short for colonel).
'in' means one lot of letters goes inside another.
'house' becomes 'semi' (short for semi-detached).
'semi'+'on'='semion'
'col' placed into 'semion' is 'SEMICOLON'.
(Other definitions for semicolon that I've seen before include "can cut sentence" , "used by writers for a break" , "half a stop" , "Joiner" , "Item of punctuation" .)