Time’s up! Destroy the first house (4)
I believe the answer is:
semi
'house' is the definition.
(semi-detached house)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for semi that I've seen before include "Co-joined house" , "The next to final round" , "One house of pair" , "half would do!" , "Property attached to another" .)