Heard of bygone times forgotten (6,2)
I believe the answer is:
passed by
'forgotten' is the definition.
(something that's passed by has been forgotten)
'heard of bygone times' is the wordplay.
'heard of' shows a homophone (sound like).
'bygone' becomes 'past' (similar in meaning).
'times' becomes 'by' (both can mean 'multiplied by').
'past' sounds like 'passed'.
'passed'+'by'='PASSED BY'
(Other definitions for passed by that I've seen before include "ignored" , "Avoided" , "The person who approved this is" .)