Abhor not having instrument (4)
I believe the answer is:
horn
'instrument' is the definition.
(horn is a kind of instrument)
'abhor not having' is the wordplay.
'having' indicates a hidden word.
'HORN' can be found hidden inside 'abhor not'.
(Other definitions for horn that I've seen before include "Instrument - rhino's appendage" , "Warning device on a vehicle" , "Head growth; cornucopia" , "Head appendage; warning instrument" , "Wind instrument - cape" .)