Delivery panic to ruin mobile working (13)
I believe the answer is:
pronunciation
'delivery' is the definition.
(thesaurus)
'panic to ruin mobile working' is the wordplay.
'mobile' indicates an anagram.
'working' becomes 'on'.
'panic'+'to'+'ruin'='panictoruin'
'panictoruin' anagrammed gives 'pronunciati'.
'pronunciati'+'on'='PRONUNCIATION'
(Other definitions for pronunciation that I've seen before include "Delivery" , "Articulation" , "Way a word is sounded" .)