Keynote backed by Conservative in Biblical reference (5)
I believe the answer is:
tonic
'keynote' is the definition.
(synonyms)
'backed by conservative in biblical reference' is the wordplay.
'backed by' means one lot of letters go next to another.
'conservative' becomes 'C' (UK political abbreviation).
'in biblical reference' becomes 'toni' (I can't explain this - if you can you should believe this answer much more).
'c' after 'toni' is 'TONIC'.
Can you help me to learn more?
(Other definitions for tonic that I've seen before include "Key" , "Invigorating medicine - keynote" , "Stimulant" , "A pick-me-up drink, nice with gin" , "Carbonated mixer" .)