British in Foreign Legion, common (7)
I believe the answer is:
ignoble
'common' is the definition.
(I've seen this in another clue)
'british in foreign legion' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'in' is an insertion indicator.
'foreign' is an anagram indicator (foreign order of the letters).
'legion' is an anagram of 'ignole'.
'b' placed inside 'ignole' is 'IGNOBLE'.
(Other definitions for ignoble that I've seen before include "Contemptible" , "Lacking dignity" , "Inferior" , "Humble; despicable" , "Completely lacking in character or purpose" .)