Nimby is one jumping on my car (7)
I believe the answer is:
acronym
'nimby is one' is the definition.
(I've seen this before)
'jumping on my car' is the wordplay.
'jumping' is an anagram indicator.
'on'+'my'+'car'='onmycar'
'onmycar' with letters rearranged gives 'ACRONYM'.
(Other definitions for acronym that I've seen before include "FBI?" , "Radar, for example" , "Eg, Nato, Sars" , "radar, for one" , "Word formed from 1st letters of other words" .)