Merriam-Webster's Collegiate® Dictionary, 11th Edition
SOBER
I. adjective (soberer; soberest)
Etymology: Middle English sobre, from Anglo-French, from Latin sobrius; akin to Latin ebrius drunk
Date: 14th century
1. sparing in the use of food and drink ; abstemious , not addicted to intoxicating drink, not drunk, marked by sedate or gravely or earnestly thoughtful character or demeanor, unhurried , calm , marked by temperance, moderation, or seriousness , subdued in tone or color, showing no excessive or extreme qualities of fancy, emotion, or prejudice, see: serious soberly adverb soberness noun
II. verb (sobered; sobering)
Date: 14th century
transitive verb to make sober, intransitive verb to become sober