Significant this compiler's British in spirit (9)
I believe the answer is:
memorable
'significant' is the definition.
(thesaurus)
'this compiler's british in spirit' is the wordplay.
'this compiler' becomes 'me' (the person who is writing these clues).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'in' indicates putting letters inside.
'spirit' becomes 'morale' (I can't justify this - if you can you should believe this answer much more).
'b' inserted into 'morale' is 'morable'.
'me'+'morable'='MEMORABLE'
Can you help me to learn more?
(Other definitions for memorable that I've seen before include "Special" , "Catchy" , "noteworthy" , "Easily recalled" .)