Spear I'd dropped in English river (7)
I believe the answer is:
trident
'spear' is the definition.
(trident is a kind of spear)
'i'd dropped in english river' is the wordplay.
'dropped in' means one lot of letters goes inside another.
'english river' becomes 'trent' (I've seen this before).
'id' put into 'trent' is 'TRIDENT'.
(Other definitions for trident that I've seen before include "Red tint? (anagram)" , "3-pronged spear" , "Neptune's fork" , "Nuclear missile" , "A three-pronged spear as wielded by Neptune" .)