Old English swerian "take an oath" (class VI strong verb; past tense swor, past participle sworen), from Proto-Germanic *swērjanan (source also of Old Saxon swerian, Old Frisian swera, Old Norse sverja, Danish sverge, Middle Dutch swaren, Old High German swerien, German schwören, Gothic swaren "to swear"), of uncertain origin, perhaps from a PIE *swer- "to speak, talk, say" (source also of Old Church Slavonic svara "quarrel," Oscan sverrunei "to the speaker").
Also related to the second element in answer. The secondary sense of "use bad language" (early 15c.) probably developed from the notion of "invoke sacred names." Swear off "desist as with a vow" is from 1898. Swear in "install (someone) in office by administration of an oath" is attested from 1700 in modern use, echoing Old English.
[Swearing and cursing] are entirely different things : the first is invoking the witness of a Spirit to an assertion you wish to make ; the second is invoking the assistance of a Spirit, in a mischief you wish to inflict. When ill-educated and ill-tempered people clamorously confuse the two invocations, they are not, in reality, either cursing or swearing ; but merely vomiting empty words indecently. True swearing and cursing must always be distinct and solemn .... [Ruskin, "Fors Clavigera"]
late 14c., farmacie, "a medicine that rids the body of an excess of humors (except blood);" also "treatment with medicine; theory of treatment with medicine," from Old French farmacie "a purgative" (13c.) and directly from Medieval Latin pharmacia, from Greek pharmakeia "a healing or harmful medicine, a healing or poisonous herb; a drug, poisonous potion; magic (potion), dye, raw material for physical or chemical processing."
This is from pharmakeus (fem. pharmakis) "a preparer of drugs, a poisoner, a sorcerer" from pharmakon "a drug, a poison, philter, charm, spell, enchantment." Beekes writes that the original meaning cannot be clearly established, and "The word is clearly Pre-Greek." The ph- was restored 16c. in French, 17c. in English (see ph).
Buck ["Selected Indo-European Synonyms"] notes that "Words for 'poison', apart from an inherited group, are in some cases the same as those for 'drug' ...." In addition to the Greek word he has Latin venenum "poison," earlier "drug, medical potion" (source of Spanish veneno, French venin, English venom), and Old English lybb.
Meaning "the use or administration of drugs" is from c. 1400; the sense of "art or practice of preparing, preserving, and compounding medicines and dispensing them according to prescriptions" is from 1650s; that of "place where drugs are prepared and dispensed" is recorded by 1833.
mid-13c., "a post in government or administration, an employment to which certain duties are attached, secular position of authority or responsibility," from Anglo-French and Old French ofice "place or function; divine service" (12c. in Old French) and directly from Latin officium "a service, kindness, favor; an obligatory service, official duty, function, business; ceremonial observance" (in Medieval Latin, "church service").
The Latin word was contracted from opificium, literally "work-doing," from ops (genitive opis) "power, might, abundance, means" (related to opus "work," from PIE root *op- "to work, produce in abundance") + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").
Of ecclesiastical positions from late 14c. From c. 1300 as "official employment" in general, also "ecclesiastical service or mass; the prescribed order and form of church services." Meaning "building or room for conducting business" is from late 14c. Meaning "a government or civic department" is from mid-15c. From 1727 as "a privy."
Office hours "hours of work in an office" is attested from 1841. Office furniture, the type used or commonly found in offices, is by 1839. The political office-holder is by 1818. Office-party, one held for the members of a staff, is by 1950. Middle English had office of life "state of being alive" (late 14c.), translating Latin vite officio.
c. 1100, "celebration of public religious worship according to prescribed forms or methods," from Old French servise "act of homage; servitude; service at table; Mass, church ceremony," from Latin servitium (in Medieval Latin also servicium) "slavery, condition of a slave, servitude," also "slaves collectively" (in Medieval Latin "service"), from servus "slave" (see serve (v.)).
The meaning "act of serving, occupation of an attendant servant" is attested from c. 1200, as is that of "assistance, help; a helpful act." From c. 1300 as "provision of food; sequence of dishes served in a meal;" from late 14c. as "service at table, attendance during a meal." The sense of "the furniture of the table" (tea service, etc.) is from mid-15c.
Meanings "state of being bound to undertake tasks for someone or at someone's direction" and "labor performed or undertaken for another" are mid-13c. The sense of "service or employment in a court or administration" is from c. 1300, as is that of "military service (especially by a knight); employment as a soldier;" hence "the military as an occupation" (1706).
The meaning "the supplying of electricity, water, gas, etc., for domestic use" is by 1879; later extended to broadcasting (1927), etc. The meaning "expert care or assistance given by manufacturers or dealers to the purchasers of their goods" is by 1919. Service industry (as distinct from production) is attested from 1938; service there indicates the section of the economy that supplies consumer needs but makes no tangible goods (a sense attested by 1936). Service-charge is attested by 1929. A service station originally was a gas stop that also repaired cars.
At your service as a phrase of politeness is attested by c. 1600. Service-book, containing forms for public worship, is attested from 1570s. Also in Middle English, service was "the devotion or suit of a lover" (late 14c.), and "sexual intercourse, conjugal relations" (mid-15c.; service of Venus, or flesh's service).