Source : Webster's Revised Unabridged Dictionary (1913)

Assiduity \As`si*du"i*ty\, n.; pl. {Assiduities}. [L.
   assiduitas: cf. F. assiduite. See {Assiduous}.]
   1. Constant or close application or attention, particularly
      to some business or enterprise; diligence.

            I have, with much pains and assiduity, qualified
            myself for a nomenclator.             --Addison.

   2. Studied and persevering attention to a person; -- usually
      in the plural.