Apodictic

Apodictic \ap-uh-DIK-tik\ , adjective;
1. Necessarily true or logically certain
2. Incontestable because of having been demonstrated or proved to be demonstrable

This word dates to the 1650's as "clearly demonstrated" from Latin apodicticus. The Latin word is taken from Greek apodeiktikos, which derives from apodeiktos, the verbal adjective of apodeiknyai. Apodeiknyai means "to show off, demonstrate," but it literally means "to point away from" from apo + deikynai ("off, away" + "to show"). Deikynai derives from Proto-Indo-European *deik- ("to point out"), which is also the forebear of diction.

Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Friday, July 15
Etymologies come from the Oxford English Dictionary and/or Etymonline.com