Pro*tac"tic (?), a. [Gr. placing or placed before, fr. to place in front; before + to arrange.]
Giving a previous narrative or explanation, as of the plot or personages of a play; introductory.
<-- Protactinium. A radioactive chemical element. Atomic symbol Pa; at. no. 91; at. wt. of longest-lived isotope, 231 (T = 32,500 yrs.) Also called brevium, Uranium X2 and UX2. -->
© Webster 1913.