The Collaborative International Dictionary of English v.0.48:

Unipersonal \U"ni*per"son*al\, a. [Uni- + personal.]
   [1913 Webster]
   1. Existing as one, and only one, person; as, a unipersonal
      God.
      [1913 Webster]

   2. (Gram.) Used in only one person, especially only in the
      third person, as some verbs; impersonal.
      [1913 Webster]