First British martyr (5)
I believe the answer is:
alban
'first british martyr' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alban that I've seen before include "First British martyr, supposedly born in Verulamium" , "Hertfordshire saint" , "First Christian martyr in England" , "Saint born at Verulamium" , "Ancient Scottish kingdom" .)