Nut that looks like a grain (5)
I believe the answer is:
acorn
'nut that looks' is the definition.
'acorn' can be an answer for 'nut' (I've seen this in another clue). I'm not certain of the remainder of the definition.
'a grain' is the wordplay.
'grain' becomes 'corn' (corn is a kind of grain).
'a'+'corn'='ACORN'
'like' is the link.
Can you help me to learn more?
(Other definitions for acorn that I've seen before include "Fruit-seed of the oak" , "Source of a great oak" , "mast" , "From which a "tall oak" may grow" , "Fruit of the oak tree" .)