Line on a letter (5)
I believe the answer is:
serif
'line on a letter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for serif that I've seen before include "Slight projection finishing off printed letter - puts fires out" , "decorative line" , "Stroke's foot" , "Little bit of character" , "Short line at the end of the main strokes of a printed character" .)