State so petty to convince of lie? (8)
I believe the answer is:
gaslight
'convince of lie?' is the definition.
I can't tell whether this defines the answer.
'state so petty' is the wordplay.
'state' becomes 'gas' (gas is a kind of state).
'so petty' becomes 'light' (I can't explain this - if you can you should believe this answer much more).
'gas'+'light'='GASLIGHT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for gaslight that I've seen before include "Old form of illumination" , "Old-fashioned illumination" , "Bergman film" , "that was illuminating for Fanny" , "Old guide in dark" .)