Scandalous information turned round American threesome (5)
I believe the answer is:
triad
'threesome' is the definition.
(I know that threesome can be written as triad)
'scandalous information turned round american' is the wordplay.
'scandalous information' becomes 'dirt' (I've seen this before).
'turned' says the letters should be written in reverse.
'round' is an insertion indicator.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'dirt' written backwards gives 'trid'.
'trid' placed around 'a' is 'TRIAD'.
(Other definitions for triad that I've seen before include "Group or set of three" , "Set of three; chord" , "trio" , "Union of three" , "Criminals" .)