An Etymological Dictionary of Astronomy and Astrophysics

1. (prep.) With the addition of.
   

2. (adj.) Additional; → positive.
   

3. (n.) An addition; a positive quantity; the → plus sign.

Etymology (EN): L. plus “more,” cognate with Gk. polys “much,” Pers. por, → full.

Etymology (PE): Bišan, from biš “much, more; great” + suffix -an, → minus.
The first component from Mid.Pers. veš “more, longer; more frequently,” related to vas “many, much” (Mod.Pers. bas);
O.Pers. vasiy “at will, greatly, utterly;” Av. varəmi “I wish,” vasô, vasə “at one’s pleasure or will,” from vas- “to will, desire, wish.”