Source : Webster's Revised Unabridged Dictionary (1913)

Registrant \Reg"is*trant\ (-trant), n. [L. registrans, p. pr.]
   One who registers; esp., one who, by virtue of securing an
   official registration, obtains a certain right or title of
   possession, as to a trade-mark.

Source : WordNet®

registrant
     n : a person who is formally entered (along with others) in a
         register (and who obtains certain rights thereby)