A board that stands out (5)
I believe the answer is:
shelf
'a board' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for shelf that I've seen before include "Rock ledge; underwater bank" , "Whereon 2 down is not!" , "grass down under" , "Ledge for holding things" , "Support for holding objects" .)