County boundary approached by member of colony (6)
I believe the answer is:
antrim
'county' is the definition.
(county of Northern Ireland)
'boundary approached by member of colony' is the wordplay.
I cannot quite see how this works, but
'boundary' could be 'rim' (rim is a kind of boundary) and 'rim' is present in the answer.
'member' could be 'ant' (I have seen 'Member of colony' mean 'ant' so perhaps 'member' could also mean 'ant') and 'ant' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for antrim that I've seen before include "NI county" , "County in Ireland's north-east" , "N Ireland county of green glens" , "Ulster county" , "18 down in Ulster" .)