Minor manufacturer failing to open plant (5)
I believe the answer is:
orris
'minor' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'manufacturer failing to open plant' is the wordplay.
'manufacturer' becomes 'or' (I can't explain this - if you can you should give a lot more credence to this answer).
'failing to open' means to remove the first letter (the opening letter is removed).
'plant' becomes 'iris' (type of flower).
'iris' with its initial letter taken away is 'ris'.
'or'+'ris'='ORRIS'
Can you help me to learn more?
(Other definitions for orris that I've seen before include "Percussion instrument" , "Iris root in perfumery" , "Fragrant rootstock" , "Type of flower" , "Fragrant iris extract" .)