Willow, large, that is facing river (5)
I believe the answer is:
osier
'willow' is the definition.
(I know that osier is a type of willow)
'large that is facing river' is the wordplay.
'large' becomes 'os' (abbreviation for oversize).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'facing' means one lot of letters go next to another.
'river' becomes 'r' (abbreviation for river).
'os'+'ie'+'r'='OSIER'
(Other definitions for osier that I've seen before include "... source of twigs to make baskets" , "Small willow; its shoot" , "Basket producer" , "one used to get weaving?" , "Basket-maker" .)