Take firm hold of bristles regularly (4)
I believe the answer is:
bite
'take firm hold' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'bristles regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'bristles' are 'BITE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for bite that I've seen before include "Get teeth into" , "Grip; take effect" , "(Of fish) take the bait" , "Cut with the teeth" , "Small amount to eat" .)