Abstemious \ab-STEE-mee-uhs\ , adjective;
1. Sparing in eating and drinking; temperate; abstinent
2. Sparing in use or consumed; used with temperance or moderation
3. Marked by or spent in abstinence.
This word dates to the 1600's from Latin abstemius ("sober, temperate"). It's a combination of ab- + temetum ("from" + "strong drink"). Temetum is related to temulentus ("drunken"). Technically the definition relates to liquor, but it's extended to general temperance in living in Latin.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Sunday, April 3
Etymologies come from the Oxford English Dictionary and/or Etymonline.com