From Latin 'abstinere' (to hold back) — someone abstinent literally holds themselves away from indulgence.
Refraining from indulgence, especially in food, drink, or sexual activity; practicing self-restraint.
From Old French 'abstinent,' from Latin 'abstinentem' (self-restraining, temperate), present participle of 'abstinēre' (to hold back, to refrain from), from 'abs-' (away from, variant of 'ab-') + 'tenēre' (to hold), from PIE *ten- (to stretch, to hold). Someone abstinent literally 'holds themselves away from' indulgence — restraining the self by keeping it at a distance from temptation. The root *ten- is extraordinarily productive: it gave Latin 'tenēre' (to hold), 'tendere' (to stretch), 'tennis' (via French 'tenez,' hold!), 'tenor' (a holding of course), 'tense,' 'tension,' and 'tendon
'Abstinent' and 'continent' are near-synonyms built from the same root with different prefixes. 'Abstinent' (holding away from) emphasizes the thing being avoided — you abstain from alcohol. 'Continent' (holding together) emphasizes self-containment — you keep yourself together. Medieval moral theology