1580s, "subject to the authority of another" (a sense now obsolete), from Latin obnoxiosus "hurtful, injurious," from obnoxius "subject, exposed to harm," from ob "to, toward" (see ob-) + noxa "injury, hurt, damage entailing liability" (from PIE root *nek- (1) "death"). Meaning "subject to something harmful, exposed to injury" is by 1590s. The main modern meaning "offensive, hateful, highly objectionable" is a shifted sense recorded from 1670s, influenced by noxious.

Obnoxious has two very different senses, one of which (exposed or open or liable to attack or injury) requires notice because its currency is now so restricted that it is puzzling to the uninstructed. It is the word's rightful or de jure meaning, and we may hope that scholarly writers will keep it alive. [Fowler]

Related: Obnoxiously; obnoxiousness.

"to darken, cloud, overcloud," 1580s, from Latin obnibulatus, past participle of obnubilare "to cover with clouds or fog," from ob "in front of, against" (see ob-) + verb from Latin nubes "cloud," from PIE *sneudh- "fog" (see nuance). Related: Obnubilated; obnubilating. Middle English had obnubilous "obscure, indistinct" (early 15c.).

"act of making dark or obscure; fact of being overclouded," c. 1600, noun of action from obnubilate (v.).

also o.b.o., abbreviation of or best offer, by 1969 in for-sale classified ads.

"wooden, double-reeded wind instrument, 1724, from Italian oboe, from phonological spelling of French hautbois (itself borrowed in English 16c. as hautboy), from haut "high, loud, high-pitched" (see haught) + bois "wood" (see bush (n.)). So called because it had the highest register among woodwind instruments. Also compare shawm. Related: Oboist (by 1830). "The tone is small, but highly individual and penetrating; it is especially useful for pastoral effects, for plaintive and wailing phrases, and for giving a reedy quality to concerted passages." [Century Dictionary]

ancient Greek small coin and weight, 1660s, from Latin obolus, from Greek obolos, the name of a coin (sixth part of a drachme); identical with obelos "a spit, needle, broach; bar of metal used as a coin or weight" (see obelisk). So called from the original shape. Middle English had obolus as the name of a small measure of weight, also ob "halfpenny," from Latin ob., abbreviation of obolus.

"the obtaining or trying to obtain something by craft or deception," 1610s, from Latin obreptionem (nominative obreptio)  "a creeping or stealing on," noun of action from past-participle stem of obrepere "to creep on, creep up to," from ob "on, to" (see ob-) + repere "to creep" (see reptile). Opposed to subreption, which is to obtain something by suppression of the truth. Related: Obreptious.

1590s, "offensive to the senses, or to taste and refinement," from Middle French obscène (16c.), from Latin obscenus "offensive," especially to modesty, originally "boding ill, inauspicious," a word of unknown origin; perhaps from ob "in front of" (see ob-) + caenum "filth."

The meaning "offensive to modesty or decency, impure, unchaste" is attested from 1590s. Legally, "any impure or indecent publication tending to corrupt the mind and to subvert respect for decency and morality." In modern U.S. law, the definition hinged on "whether to the average person, applying contemporary community standards, the dominant theme of the material taken as a whole appeals to a prurient interest." [Justice William Brennan, "Roth v. United States," June 24, 1957]; this was refined in 1973 by "Miller v. California":

The basic guidelines for the trier of fact must be: (a) whether 'the average person, applying contemporary community standards' would find that the work, taken as a whole, appeals to the prurient interest, (b) whether the work depicts or describes, in a patently offensive way, sexual conduct specifically defined by the applicable state law; and (c) whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.

Related: Obscenely.

1580s, "obscene quality, lewdness in action, expression, or representation," from French obscénité, from Latin obscenitatem (nominative obscenitas) "inauspiciousness, filthiness," from obscenus "offensive" (see obscene). Meaning "a foul or loathsome act" is 1610s. Sense of "an obscene utterance or word" is attested by 1690. Related: Obscenities.

"that obscures or darkens; that labors to prevent enlightenment," 1804, from French obscurant, from Latin obscurantem (nominative obscurans), present participle of obscurare "to make dark, darken, obscure," from obscurus (see obscure (adj.)).