Commonly Used Latin Words and Phrases in Modern English

In his book A Natural History of Latin (OUP 2004, p.173), linguist Tore Janson remarks that "English is a Germanic language which mainly consists of words that are not Germanic." English and Latin share a long and varied history that started in 43 A.D., when the Roman Emperor Claudius invaded Britain, and culminated in 1066 with the Norman Conquest. Latin roots, words, and phrases entered English either directly or through French, and enriched it in a manner that no other language parallels. Words of Latin origin range from everyday vocabulary (village, mountain, street, pillow, pear, sock, noon, people, peace, cup, kitchen) and common abbreviations (a.m., p.m., etc., PhD, i.e., e.g.) to vocabulary pertaining to a more learned register (malfeasance, aberrant, quintessential, gregarious, attrition, ubiquitous) and medical terminology (ocular, percutaneous, antecubital, coagulation).

Because of the strong dual tradition (Germanic and Latin), English is rich in "lexical alternatives", i.e. word couples of Germanic vs. Latin origin, that mean the same... well, almost: happiness/felicity, pig/pork, work/labor, height/altitude, ask/interrogate, start/commence. Because of this dual tradition, the Old English cealf (calf) can only be served as the Latin vitellus (veal).

The following list is a sampler of (more or less) commonly used Latin words and phrases in modern English.

ab ovo (literally "from the egg"): from the beginning, esp. with reference to a narrative

ad hoc (literally "towards this"): for this, for a particular purpose only

ad infinitum (literally "to infinity"): without end, indefinitely

ad nauseam (literally "to the point of sickness"): in reference to something that is repeated excessively and as a result becomes sickening

alma mater (Latin for "bountiful mother"): one's former school, college, or university; the official song (hymn) of a college or university

caveat emptor (Latin for "let the buyer beware"): the buyer is responsible for the quality of the merchandise she buys

circa (Latin for "around" (cf. circular, circus); literally "surrounding"): about (in a chronological sense), approximately; usually in reference to dates: died circa 1400

curriculum vitae (literally "course of life"): a concise account of one's education, qualifications, and jobs previously held; a resume (US)

de gustibus disputandum non est (literally "there is no disputing about tastes"): there is no accounting for taste

deus ex machina (literally "a god from a machine"): originally referring to a device in ancient Greek theater used to suspend the actor in the role of god, the phrase now has the figurative meaning of a narrative device that unexpectedly (and very conveniently) resolves a plot; (very bad idea in screenwriting, by the way)

ex cathedra (literally "from the seat"): decisively, authoritatively, from a position of power and authority

in flagrante delicto (literally "with the crime blazing"): (to be caught) red-handed

in memoriam (Latin for "in memory"): in memory of

in vino veritas (literally "in wine (there is) the truth"): intoxication loosens many a tongue...

in vitro (literally "in glass"): in an artificial environment; cf. in vivo

in vivo (literally "in the living"): inside a living body; cf. in vitro

modus operandi (Latin for "mode of working"): a characteristic method, a procedure typically followed by someone (esp. a criminal)

non sequitur (literally "it does not follow"): an illogical or irrelevant statement

paterfamilias (Latin for "male head of the household"): the father of a family

quid pro quo (literally "something for something"): a favor in exchange for a favor; also Dr Hannibal Lecter's modus operandi

sine qua non (literally "without which not"): an indispensable factor

status quo (literally "condition in which"): the present state of affairs

subpoena (Latin for "under penalty": sub poena): an official notification to appear in court; the writ bears the warning "under penalty", sub poena

sui generis (literally "of its own kind"): unique

verbatim (Latin for "word for word"; from verbum = word): (quoted) exactly

Sources:

Merriam-Webster Online: http://www.m-w.com

A Natural History of Latin by Tore Janson (OUP 2004)

http://www.associatedcontent.com/article/197515/common_latin_abbreviations.html