One of a poetic host's urns is cast almost sloppily (9)
I believe the answer is:
narcissus
'one of a poetic host's' is the definition.
('A host of golden daffodils' - William Wordsworth)
'urns is cast almost sloppily' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'sloppily' is an anagram indicator (I've seen this in other clues).
'urns'+'is'+'cast'='urnsiscast'
'urnsiscast' with its last letter taken off is 'urnsiscas'.
'urnsiscas' with letters rearranged gives 'NARCISSUS'.
(Other definitions for narcissus that I've seen before include "Flower like daffodil" , "Small daffodil" , "Mythical egotist" , "Garden flower - youth of Greek mythology" , "Legendary egotist" .)