Middle English abiden, from Old English abidan, gebidan "remain, wait, wait for, delay, remain behind," from ge- completive prefix (denoting onward motion; see a- (1)) + bidan "bide, remain, wait, dwell" (see bide).
Originally intransitive (with genitive of the object: we abidon his "we waited for him"); the transitive senses of "endure, sustain, stay firm under," also "tolerate, bear, put up with" (now usually with a negative) are from c. 1200. To abide with "stay with (someone); live with; remain in the service of" is from c. 1300.
Related: Abided; abiding. The historical conjugation was abide, abode, abidden, but in Modern English the formation generally is weak.
late 14c., "state or condition of being able; capacity to do or act," from Old French ableté "ability (to inherit)," from Latin habilitatem (nominative habilitas, in Medieval Latin abilitas) "aptitude, ability," noun of quality from habilis "easy to manage, handy" (see able). One case where a Latin silent -h- failed to make a return in English (despite efforts of 16c.-17c. scholars); see H. Also in Middle English, "suitableness, fitness." Abilities "one's talents or mental endowments" is from 1580s.