Fruit article — I’m surprised inwardly (5)
I believe the answer is:
acorn
'fruit' is the definition.
(acorn is a kind of fruit)
'article i'm surprised inwardly' is the wordplay.
'article' becomes 'an' (indefinite article).
'i'm surprised' becomes 'cor' (old-fashioned UK expression of shock or awe).
'inwardly' means one lot of letters goes inside another.
'an' enclosing 'cor' is 'ACORN'.
(Other definitions for acorn that I've seen before include "Might source" , "oak's fruit" , "fruit in a cup" , "Tree seed" , "Nut of oak tree" .)