An Etymological Dictionary of Astronomy and Astrophysics

Free from doubt as to the reliability, character, action, etc., of something (Dictionary.com).

Etymology (EN): M.E. sur(e), from M.Fr. sur, O.Fr. seur “safe, secure; trustworthy,” from L. securus “free from care, untroubled, safe,” from *se cura, from se “free from” + cura “care.”

Etymology (PE): Tenz, from (Fine-e Bandar Abbâs) tenz “firm, fixed, solid,” variant tereng; (Tabari) tereng, təreq “firm, fixed;” (Baxtiyâri) teng “firm;” cf. Baluci tranj-, dranjit, tranjit/drannj-, draht, dratk “to hang up;” ultimately from Proto-Ir. *dra(n)j- “to fix, fasten, hold;”
Av. drənj- (draž-) “to fix, fasten, hold;” Parthian (*abi-) ‘bdrynj- “to be sure, secure; make certain;” Khotanese drys- “to hold;” cognate with Gk. drassomai “I hold (with the hand), take;” O.Irish dringid “he climbs;” M.Welsh dringo “to climb;” PIE *dreg^h- “to hold, fasten.”