About a factor having a chemical effect (7)
I believe the answer is:
reagent
'a chemical effect' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'about a factor' is the wordplay.
'about' becomes 're' (regarding).
'a factor' becomes 'agent' (I've seen this before).
're'+'agent'='REAGENT'
'having' acts as a link.
Can you help me to learn more?
(Other definitions for reagent that I've seen before include "will cause some reaction" , "Chemical with known properties" , "Chemically-active substance" , "Substance with characteristic reactions, used as a chemical test" , "What causes change" .)