Continental river accommodating slender shrub (8)
I believe the answer is:
oleander
'shrub' is the definition.
(thesaurus)
'continental river accommodating slender' is the wordplay.
'continental river' becomes 'oder' (German river).
'accommodating' indicates putting letters inside.
'slender' becomes 'lean' ('lean' can be similar in meaning to 'slender').
'oder' enclosing 'lean' is 'OLEANDER'.
(Other definitions for oleander that I've seen before include "bloomer" , "'Adorn eel, badly, with this shrub (8)'" , "Adore Len (anag.)" , "tree" , "Poisonous evergreen shrub with white, pink or red flowers" .)