Sour berries primarily found beneath tree (5)
I believe the answer is:
acerb
'sour' is the definition.
(similar in meaning)
'berries primarily found beneath tree' is the wordplay.
'primarily' says to take the initial letters.
'found beneath' means one lot of letters go next to another (I've seen this in other clues).
'tree' becomes 'acer' (acer is a type of tree).
The initial letter of 'berries' is 'b'.
'b' put after 'acer' is 'ACERB'.
(Other definitions for acerb that I've seen before include "Sour, bitter" , "harsh and bitter" , "sharp" , "tart" .)