Particles used to reconstruct moats (5)
I believe the answer is:
atoms
'particles' is the definition.
('atom' can be a synonym of 'particle')
'to reconstruct moats' is the wordplay.
'to reconstruct' indicates anagramming the letters (I've seen this in other clues).
'moats' anagrammed gives 'ATOMS'.
'used' is the link.
(Other definitions for atoms that I've seen before include "Dots" , "Small particles" , "Jots" , "Minute particles" , "small fragments" .)