A measure of resistance (3)
I believe the answer is:
ohm
This clue is a double definition.
'a measure' is the first definition.
(ohm is a kind of measure)
'resistance' is the second definition.
(thesaurus)
'of' acts as a link.
(Other definitions for ohm that I've seen before include "measure of resistance" , "SI unit of electrical resistance" , "lawmaker" , "A little resistance" , "physical unit" .)