Threesome laid into Irishman, defender of country's honour (7)
I believe the answer is:
patriot
'defender of country's honour' is the definition.
'patriot' can be an answer for 'defender' (I have seen 'Defender of country' mean 'patriot' so perhaps 'defender' could also mean 'patriot'). I am not sure about the 'of country's honour' bit.
'threesome laid into irishman' is the wordplay.
'threesome' becomes 'trio' (both can mean a group of three).
'laid into' means one lot of letters goes inside another.
'irishman' becomes 'Pat' (Patrick is a common Irish name).
'trio' placed inside 'pat' is 'PATRIOT'.
Can you help me to learn more?
(Other definitions for patriot that I've seen before include "Loyal citizen" , "One loving their country" , "One who loves his or her country" , "Defender of country" , "Loyalist" .)