Set to import outsize piano, that's true (6)
I believe the answer is:
gospel
'true' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'set to import outsize piano' is the wordplay.
'set' becomes 'gel' (both can mean to harden).
'to import' indicates putting letters inside.
'outsize' becomes 'os'.
'piano' becomes 'p' (musical abbreviation).
'os'+'p'='osp'
'gel' placed around 'osp' is 'GOSPEL'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for gospel that I've seen before include "Absolute truth" , "Christian doctrine" , "sacred text" , "Type of music" , "One in quartet" .)