Disorder in dingy port needs some backing (7)
I believe the answer is:
entropy
'disorder' is the definition.
(thesaurus)
'dingy port needs some backing' is the wordplay.
'some' indicates the answer is hidden within the clue.
'backing' shows that the letters should be reversed in order.
'yportne' is hidden within 'dingy port needs'.
'yportne' reversed gives 'ENTROPY'.
'in' is the link.
(Other definitions for entropy that I've seen before include "Degree of disorder (physics)" , "state of increasing disorder" , "Random quality" , "Physical quantity linked to disorder" , "Tory pen (anag) - measure of disorder" .)