Particle has complicated route between two points (7)
I believe the answer is:
neutron
'particle' is the definition.
(type of sub-atomic particle)
'complicated route between two points' is the wordplay.
'two points' means two replacements for 'point'.
'complicated' indicates anagramming the letters (a complex or confusing ordering of the letters).
'between' means one lot of letters goes inside another.
'point' becomes 'n'.
'point' becomes 'n'.
'route' with letters rearranged gives 'eutro'.
'n'+'n'='nn'
'eutro' going within 'nn' is 'NEUTRON'.
'has' acts as a link.
(Other definitions for neutron that I've seen before include "Turn one (anag) - kind of bomb" , "Subatomic particle with no electric charge" , "Uncharged atomic particle" , "Chargeless particle" , "Particle that decays when released" .)