Small mark or spot (5)
I believe the answer is:
speck
This clue is a double definition.
'small mark' is the first definition.
(I've seen this before)
'spot' is the second definition.
(I know that speck is a type of spot)
(Other definitions for speck that I've seen before include "smoked ham" , "Bit of dust" , "Dot" , "Italian ham" , "Tiny spot" .)