Etymology: < -able suffix + -ly suffix2, after adverbs in -ly suffix2 formed on adjectives in -able suffix, as e.g. amiably adv., honourably adv., notably adv., perdurably adv., etc.The ending -ably is found (earliest in the 13th cent.) in a large number of adverbs corresponding to adjectives in -able suffix. With such instances compare Anglo-Norman and Old French, Middle French, French -ablement (formations in which are found from at least the late 12th cent.). Subsequently, by analogy with such adverbial formations, -ably came to be used to form adverbs directly < nouns, verbs, or adjectives in cases where no corresponding adjective in -able suffix was attested, either at all (e.g. meanably adv., pausably adv.), or in a relevant sense (e.g. occasionably adv., personably adv.). In some cases an adjective is recorded in the relevant sense but only at a later date (e.g. murderably adv.). Such formations are attested sporadically from the late Middle English period, apparently earliest in personably adv. and murderably adv. The majority of formations are from nouns; formations from adjectives (e.g. meanably adv.) or from verbs (e.g. pausably adv.) are rarer.
This entry has been updated (OED Third Edition, September 2009; most recently modified version published online December 2020).