Supposed to have gone on to the piano (8)
I believe the answer is:
presumed
'supposed' is the definition.
(I've seen this before)
'gone on to the piano' is the wordplay.
I cannot really see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
'piano' could be 'p' (musical abbreviation) and 'p' is found within the answer.
This explanation may well be incorrect...
'to have' is the link.
Can you help me to learn more?
(Other definitions for presumed that I've seen before include "thought" , "Took for granted" , "Supposed" , "Taken for granted" , "Was impertinent" .)