The Collaborative International Dictionary of English v.0.48:

Hollyhock \Hol"ly*hock\, n. [OE. holihoc; holi holy + hoc
   mallow, AS. hoc; cf. W. hocys mallows, hocys bendigaid
   hollyhock, lit., blessed mallow. Prob. so named because
   brought from the Holy Land. See Holy.] (Bot.)
   A species of Alth[ae]a (Alth[ae]a rosea), bearing flowers
   of various colors; -- called also rose mallow.

   Note: Rose mallow is listed as a variety of Hibiscus, not
         Hollyhock in several Web pages. Name change???
         [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

hollyhock
    n 1: any of various plants of the genus Althaea; similar to but
         having smaller flowers than genus Alcea [syn: althea,
         althaea, hollyhock]
    2: any of various tall plants of the genus Alcea; native to the
       Middle East but widely naturalized and cultivated for its
       very large variously colored flowers