Helpful Heather is fire starter (8)
I believe the answer is:
kindling
'fire starter' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'helpful heather' is the wordplay.
'helpful' becomes 'kind' (similar in meaning).
'heather' becomes 'ling' (synonyms).
'kind'+'ling'='KINDLING'
'is' is the link.
Can you help me to learn more?
(Other definitions for kindling that I've seen before include "Material for starting fires" , "Fire-lighting material" , "Material for starting a fire" , "Tinder" , "Fire-starting material" .)