Foreign weed given to British fool (5)
I believe the answer is:
dweeb
'fool' is the definition.
(I've seen this before)
'foreign weed given to british' is the wordplay.
'foreign' indicates an anagram (foreign order of the letters).
'given to' says to put letters next to each other.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'weed' with letters rearranged gives 'dwee'.
'dwee'+'b'='DWEEB'
(Other definitions for dweeb that I've seen before include "Boringly studious student" , "Insignificant student" , "Fool" , "misfit" , "(US) idiot" .)