The Collaborative International Dictionary of English v.0.48:

Speculator \Spec"u*la`tor\ (sp[e^]k"[-u]*l[=a]`t[~e]r), n. [L.,
   a spy, explorer, investigator: cf. F. sp['e]culateur.]
   One who speculates. Specifically:
   (a) An observer; a contemplator; hence, a spy; a watcher.
       [Obs.] --Sir T. Browne.
       [1913 Webster]
   (b) One who forms theories; a theorist.
       [1913 Webster]

             A speculator who had dared to affirm that the human
             soul is by nature mortal.            --Macaulay.
       [1913 Webster]
   (c) (Com.) One who engages in speculation; one who buys and
       sells goods, land, etc., with the expectation of deriving
       profit from fluctuations in price.
       [1913 Webster]

WordNet (r) 3.0 (2006):

speculator
    n 1: someone who makes conjectures without knowing the facts
    2: someone who risks losses for the possibility of considerable
       gains [syn: speculator, plunger]