A very loud lecture outside on platform (8)
I believe the answer is:
scaffold
'platform' is the definition.
(scaffold is a kind of platform)
'a very loud lecture outside' is the wordplay.
'very loud' becomes 'ff' (musical abbreviation).
'lecture' becomes 'scold'.
'outside' indicates putting letters inside.
'a'+'ff'='aff'
'aff' inserted into 'scold' is 'SCAFFOLD'.
'on' acts as a link.
(Other definitions for scaffold that I've seen before include "Platform refreshment" , "Temporary structure around a building" , "where many died" , "Temporary erection for workmen - gallows" , "Framework of poles and planks on construction site" .)