abstainyoudaoicibaDictYouDict[abstain 词源字典]
abstain: [14] The literal meaning of this word’s ultimate source, Latin abstinēre, was ‘hold or keep away’, and hence ‘withhold’ (the root verb, tenēre, produced many other derivatives in English, such as contain, maintain, obtain, and retain, as well as tenacious, tenant, tenement, tenet, tenor, and tenure).

That is how it was used when it was first introduced into English (via Old French abstenir), and it was not until the 16th century that it began to be used more specifically for refraining from pleasurable activities, particularly the drinking of alcohol. The past participial stem of the Latin verb, abstent-, gave us abstention, while the present participial stem, abstinent-, produced abstinent and abstinence.

There is no connection, incidentally, with the semantically similar abstemious, which comes from a Latin word for alcoholic drink, tēmōtum.
[abstain etymology, abstain origin, 英语词源]
absent (v.)youdaoicibaDictYouDict
"to keep away" (from), c. 1400, from Middle French absenter, from Late Latin absentare "cause to be away," from Latin absentem (see absent (adj.)). Related: Absented; absenting.
exercise (n.)youdaoicibaDictYouDict
mid-14c., "condition of being in active operation; practice for the sake of training," from Old French exercice (13c.) "exercise, execution of power; physical or spiritual exercise," from Latin exercitium "training, exercise" (of soldiers, horsemen, etc.); "play;" in Medieval Latin also of arts, from exercitare, frequentative of exercere "keep busy, keep at work, oversee, engage busily; train, exercise; practice, follow; carry into effect; disturb, disquiet," literally "remove restraint," from ex- "off" (see ex-) + arcere "keep away, prevent, enclose," from PIE *ark- "to hold, contain, guard" (see arcane).

Original sense may have been driving farm animals to the field to plow. Meaning "physical activity for fitness, etc." first recorded in English late 14c. Also from late 14c. as "a carrying out of an action; a doing or practicing; a disciplinary task." In reference to written schoolwork from early 17c. The ending was abstracted for formations such as dancercise (1967); jazzercise (1977); and boxercise (1985).