Cylinder right for a potato, say (5)
I believe the answer is:
tuber
'for a potato say' is the definition.
(type of tuber)
'cylinder right' is the wordplay.
'cylinder' becomes 'tube' (tube is a kind of cylinder).
'right' becomes 'r' (common abbreviation).
'tube'+'r'='TUBER'
(Other definitions for tuber that I've seen before include "Root eg of potato" , "Fleshy underground part of plant" , "A potato, for instance" , "Fleshy underground stem (eg of the potato)" , "Fleshy underground root" .)