Particle -- turn one out (7)
I believe the answer is:
neutron
'particle' is the definition.
(neutron is a kind of particle)
'turn one out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'turn'+'one'='turnone'
'turnone' with letters rearranged gives 'NEUTRON'.
(Other definitions for neutron that I've seen before include "Subatomic particle with no electric charge" , "one's not charged" , "Particle that decays when released" , "one isn't charged" , "Uncharged atomic particle" .)