Interjector is a flax comber (7)
I believe the answer is:
heckler
This might be a double definition.
'interjector' is the first definition.
Both the definition and answer are singular nouns.
Perhaps there's an association between them I don't understand?
'flax comber' is the second definition.
The definition suggests a singular noun which matches the answer.
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for heckler that I've seen before include "One interrupts a public speaker with abusive comments" , "Unruly audience member" , "Person who jeers speaker from the crowd" , "One interrupting speech" , "One barracking a public speaker" .)