Source : Webster's Revised Unabridged Dictionary (1913)

Theorize \The"o*rize\, v. i. [imp. & p. p. {Theorized}; p. pr. &
   vb. n. {Theorizing}.] [Cf. F. th['e]oriser.]
   To form a theory or theories; to form opinions solely by
   theory; to speculate.