The Collaborative International Dictionary of English v.0.48:

nationalist \na"tion*al*ist\, n.
   1. One who advocates national unity and independence; -- as,
      for example, one of a party favoring Irish independence
      before 1918.
      [1913 Webster +PJC]

   2. One who advocates nationalism, in any sense.
      [PJC]

WordNet (r) 3.0 (2006):

nationalist
    adj 1: devotion to the interests or culture of a particular
           nation including promoting the interests of one country
           over those of others; "nationalist aspirations"; "minor
           nationalistic differences" [syn: nationalist,
           nationalistic]
    n 1: one who loves and defends his or her country [syn:
         patriot, nationalist]
    2: an advocate of national independence of or a strong national
       government