The Collaborative International Dictionary of English v.0.48:

Schismatic \Schis*mat"ic\ (s[i^]z*m[a^]t"[i^]k; so nearly all
   orthoepists), a. [L. schismaticus, Gr. ?: cf. F.
   schismatique.]
   Of or pertaining to schism; implying schism; partaking of the
   nature of schism; tending to schism; as, schismatic opinions
   or proposals.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Schismatic \Schis*mat"ic\ (?; 277), n.
   One who creates or takes part in schism; one who separates
   from an established church or religious communion on account
   of a difference of opinion. "They were popularly classed
   together as canting schismatics." --Macaulay.
   [1913 Webster]

   Syn: Heretic; partisan. See Heretic.
        [1913 Webster]

WordNet (r) 3.0 (2006):

schismatic
    adj 1: of or relating to or involved in or characteristic of
           schism; "schismatic sects" [syn: schismatic,
           schismatical]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "schismatic":
   Young Turk, apostate, backslider, bolter, breakaway,
   collaborationist, collaborator, convert, defector, demurrer,
   denominationalist, deserter, dissenter, dissentient, dissident,
   divisive, factionist, fifth columnist, heretical, heterodox,
   misbeliever, mugwump, nonconformist, objector, opinionist,
   opposition voice, proselyte, protestant, protester, quisling,
   radical, rebellious, recidivist, recreant, recusant, renegade,
   renegado, renegate, reversionist, runagate, schismatical, seceder,
   secessionist, sectarian, sectary, separatist, skeptic,
   strikebreaker, tergiversant, tergiversator, traitor, turnabout,
   turncoat, turntail, unconventional, unorthodox