English words of Greek origin

The Greek language has contributed to the English vocabulary in three ways:
 * 1) directly as an immediate donor,
 * 2) indirectly through other intermediate language(s), as an original donor (mainly through Latin and French), and
 * 3) modern coinages using Greek roots.

Overview
The contribution of Greek to the English vocabulary can be quantified in two ways, type and token frequencies: type frequency is the proportion of distinct words; token frequency is the proportion of words in actual texts.

Since most words of Greek origin are specialized technical and scientific coinages, the type frequency is considerably higher than the token frequency. And the type frequency in a large word list will be larger than that in a small word list. In a typical English dictionary of 80,000 words, which corresponds very roughly to the vocabulary of an educated English speaker, about 5% of the words are borrowed from Greek directly, and about 25% indirectly (if we count modern coinages from Greek roots as Greek).

Since the living Greek and English languages were not in direct contact until modern times, borrowings were necessarily indirect, coming either through Latin (through texts or various vernaculars), or from Ancient Greek texts, not the living language. More recently, a huge number of scientific, medical, and technical neologisms have been coined from Greek roots&mdash;and often re-borrowed back into Modern Greek.

Still, there are a few Greek words which were borrowed organically&mdash;though indirectly. The English word olive comes through the Romance from the Latin word olīva, which in turn comes from the Greek (elaíwā). This must have been an early borrowing, since the Latin v reflects a still-pronounced digamma. The Greek word was in turn apparently borrowed from a pre-Indo-European Mediterranean substrate (see also Greek substrate language), although the earliest attested form of it is the Mycenaean Greek e-ra-wa (transliterated as "elava"), attested in Linear B syllabic script. A later Greek word, (bouturon), either borrowed from or calqued on a Scythian word, becomes Latin butyrum and eventually English butter. A larger group of early borrowings, again transmitted first through Latin, then through various vernaculars, comes from Christian language: bishop from ἐπίσκοπος (epískopos 'overseer'), priest from πρεσβύ̄τερος (presbū́teros 'elder'), and church from κῡριακόν (kȳriakón). Unlike later borrowings, which came from a written, learned tradition, olive, bishop, and so on were transmitted through vernaculars, so their English spelling does not reflect their Greek forms.

Until the 16th century, the few Greek words that were absorbed into English came through their Latin derivatives. Most of the early borrowings are for expressions in theology for which there were no English equivalents. In the late 16th century an influx of Greek words were derived directly, in intellectual fields and the new science.

In the 19th and 20th centuries a few learned words and phrases were introduced using a more or less direct transliteration of Ancient Greek (rather than the traditional Latin-based orthography) for instance nous (νοῦς), hoi polloi (οἱ πολλοί).

Finally with the growth of tourism, some words, mainly reflecting aspects of current Greek life, have been introduced with orthography reflecting Modern Greek, for instance taverna.

The written form of Greek words in English
Greek words borrowed through the literary tradition (not butter and bishop) are often recognizable from their spelling. Already in Latin, there were specific conventions for borrowing Greek. So Greek was written as 'y',  as 'æ',  as 'œ',  as 'ph', etc. These conventions (which originally reflected differences in pronunciation) have carried over into English and other languages with historical orthography (like French). They make it possible to recognize words of Greek origin, and give hints as to their pronunciation and inflection.

The Ancient Greek diphthongs and  may be spelled in three different ways in English: the digraphs ae and oe; the ligatures æ and œ; or the simple letter e. Both the digraphs and ligatures are uncommon in American usage, but the digraphs remain common in British usage. Examples are: encyclopaedia /encyclopædia / encyclopedia, haemoglobin / hæmoglobin / hemoglobin, oedema / œdema / edema, Oedipus / Œdipus / Edipus (rare). The verbal ending is spelled -ize in American English and -ise or -ize in British English.

In some cases, a word's spelling clearly shows its Greek origin. If it includes ph or includes y between consonants, it is very likely Greek. If it includes rrh, phth, or chth; or starts with hy-, ps-, pn-, or chr-; or the rarer pt-, ct-, chth-, rh-, x-, sth-, mn-, or bd-, then it is with very few exceptions Greek. One exception is ptarmigan, which is from a Gaelic word, the p having been added by false etymology.

In English, Greek prefixes and suffixes are usually attached to Greek stems, but some have become productive in English, and will combine with other stems, so we now have not only metaphor (direct borrowing from genuine ancient Greek word) and metamathematics (modern coinage using Greek roots), but also metalinguistic (Greek prefix, Latin stem).

In clusters such as ps- at the start of a word, the usual English pronunciation drops the first consonant (e.g. psychology); initial x- is pronounced z. Ch is pronounced like k rather than as in "church" (e.g. character, chaos). Consecutive vowels are often pronounced separately rather than forming a single vowel sound or one of them becoming silent (e.g. "theatre" vs. "feat").

Plurals
The plurals of learned Greek-derived words sometimes follow the Greek rules: phenomenon, phenomena; tetrahedron, tetrahedra; crisis, crises; hypothesis, hypotheses; stigma, stigmata; topos, topoi; cyclops, cyclopes; but often do not: colon, colons not *cola (except for the very rare technical term of rhetoric); pentathlon, pentathlons not *pentathla; demon, demons not *demones. Usage is mixed in some cases: schema, schemas or schemata; lexicon, lexicons or lexica; clitoris, clitorises or clitorides. And there are misleading cases: pentagon comes from Greek pentagonon, so its plural cannot be *pentaga; it is pentagons (Greek πεντάγωνα/pentagona).