Abridged tune - it's 'Under Pressure (10,3)
I believe the answer is:
compressed air
'pressure' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'abridged tune it's 'under' is the wordplay.
'abridged' becomes 'compressed' (I've seen this before).
'tune' becomes 'air' (air can mean a piece of music).
'it's 'under' says to put letters next to each other (in a down clue, some letters go below others).
'compressed'+'air'='COMPRESSED AIR'
Can you help me to learn more?
(Other definitions for compressed air that I've seen before include "that's piped" , "Something provided on garage forecourt" , "Tyre filler" , "Filler for tyres" .)