Flower pot almost useless (6)
I believe the answer is:
crocus
'flower' is the definition.
(thesaurus)
'pot almost useless' is the wordplay.
'pot' becomes 'crock' (I have seen 'Large pot' mean 'crock' so perhaps 'pot' could also mean 'crock').
'almost' means to remove the last letter (most of the word but not all of it).
'useless' becomes 'us' (abbreviation for unserviceable).
'crock' with its last letter removed is 'croc'.
'croc'+'us'='CROCUS'
(Other definitions for crocus that I've seen before include "Occurs (anag.)" , "Occurs (anagram)" , "Small pretty spring flower, yellow or white" , "Small plant with yellow, purple or white flowers" , "Slow transition" .)