Relative presses old investigators about scrap (7)
I believe the answer is:
modicum
'scrap' is the definition.
(thesaurus)
'relative presses old investigators about' is the wordplay.
'relative' becomes 'mum' (mum is a kind of relative).
'presses' indicates putting letters inside (some letters are pressed between others).
'old' becomes 'o' (abbreviation).
'investigators' becomes 'CID' (Criminal Investigation Department).
'about' is a reversal indicator.
'cid' in reverse letter order is 'dic'.
'o'+'dic'='odic'
'mum' going around 'odic' is 'MODICUM'.
(Other definitions for modicum that I've seen before include "Token amount" , "Tad" , "I cod Mum into providing a small quantity" , "Moderate quantity" , "Little bit" .)