If you "abstain," you're consciously and usually with effort choosing to "hold back" from doing something that you would like to do. So it's no surprise that "abstain" traces back through Middle English and Anglo-French to the Latin abstinēre, which combines the prefix ab- ("from, away, off") with "tenēre," a Latin verb meaning "to hold." "Tenēre" has many offspring in English - other descendants include "contain," "detain," "maintain," "obtain," "pertain," "retain," and "sustain," as well as some words that don't end in "-tain," such as "tenacious." "Abstain," like many of its cousins, has been used by English speakers since at least the 14th century.