Fresh brush undergrowth (5)
I believe the answer is:
shrub
'undergrowth' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'fresh brush' is the wordplay.
'fresh' indicates an anagram (a fresh re-ordering of the letters).
'brush' anagrammed gives 'SHRUB'.
Can you help me to learn more?
(Other definitions for shrub that I've seen before include "Perhaps Heather" , "Mixed drink of rum, sugar, fruit-juice and spice" , "Drink of rum, fruit juice and spices" , "box, say" , "Low woody perennial type of plant" .)