Land a knockout for some reason (5)
I believe the answer is:
korea
'land' is the definition.
(Korea is an example)
'a knockout for some reason' is the wordplay.
'a knockout' becomes 'ko' (synonyms).
'for some reason' becomes 'rea' (I can't explain this - if you can you should give a lot more credence to this answer).
'ko'+'rea'='KOREA'
Can you help me to learn more?
(Other definitions for korea that I've seen before include "Former Asian country" , "Eastern country" , "divided land" , "Country (North/South)" , "Asian territory, two countries" .)