In shape and size one is very like another (3)
I believe the answer is:
pea
'one is very like another' is the definition.
I can't tell whether this definition defines the answer.
'in shape and size' is the wordplay.
'in' indicates the answer is hidden within the clue.
'PEA' is hidden within 'shape and size'.
Can you help me to learn more?
(Other definitions for pea that I've seen before include "Seed eaten as vegetable" , "Little green vegetable" , "Tiny stone" , "It grows in a pod" , "12 in a pod" .)