The English vocabulary has changed considerably over the centuries.

Like many languages deriving from Proto-Indo-European (PIE), many of the most common words in English can trace back their origin (through the Germanic branch) to PIE. Such words include the basic pronouns I, from Old English ic, (cf. German Ich, Gothic ik, Latin ego, Greek ego, Sanskrit aham), me (cf. German mich, mir, Gothic mik, mīs, Latin me, Greek eme, Sanskrit mam), numbers (e.g. one, two, three, cf. Dutch een, twee, drie, Gothic ains, twai, threis (þreis), Latin unus, duo, tres, Greek oinos "ace (on dice)", duo, treis), common family relationships such as mother, father, brother, sister etc. (cf. Dutch moeder, Greek meter, Latin mater, Sanskrit matṛ; mother), names of many animals (cf. German Maus, Dutch muis, Sanskrit mus, Greek mys, Latin mus; mouse), and many common verbs (cf. Old High German knājan, Old Norse knā, Greek gignōmi, Latin gnoscere, Hittite kanes; to know).

Germanic words (generally words of Old English or to a lesser extent Old Norse origin) tend to be shorter than Latinate words, and are more common in ordinary speech, and include nearly all the basic pronouns, prepositions, conjunctions, modal verbs etc. that form the basis of English syntax and grammar. The shortness of the words is generally due to syncope in Middle English (e.g. OldEng hēafod > ModEng head, OldEng sāwol > ModEng soul) and to the loss of final syllables due to stress (e.g. OldEng gamen > ModEng game, OldEng ǣrende> ModEng errand), not because Germanic words are inherently shorter than Latinate words. (The lengthier, higher-register words of Old English were largely forgotten following the subjugation of English after the Norman Conquest, and most of the Old English lexis devoted to literature, the arts, and sciences ceased to be productive when it fell into disuse. Only the shorter, more direct, words of Old English tended to pass into the Modern language.) Consequently, those words which tend to be regarded as elegant or educated in Modern English are usually Latinate. However, the excessive use of Latinate words is considered at times to be either pretentious or an attempt to obfuscate an issue. George Orwell's essay "Politics and the English Language", considered an important scrutinisation of the English language, is critical of this, as well as other perceived misuses of the language.

An English speaker is in many cases able to choose between Germanic and Latinate synonyms: come or arrive; sight or vision; freedom or liberty. In some cases, there is a choice between a Germanic derived word (oversee), a Latin derived word (supervise), and a French word derived from the same Latin word (survey); or even words derived from Norman French(e.g., warranty) and Parisian French (guarantee), and even choices involving multiple Germanic and Latinate sources are possible: sickness (Old English), ill (Old Norse), infirmity(French), affliction (Latin). Such synonyms harbor a variety of different meanings and nuances. Yet the ability to choose between multiple synonyms is not a consequence of French and Latin influence, as this same richness existed in English prior to the extensive borrowing of French and Latin terms. Old English was extremely resourceful in its ability to express synonyms and shades of meaning on its own, in many respects rivaling or exceeding that of Modern English (synonyms numbering in the thirties for certain concepts were not uncommon). Take for instance the various ways to express the word "astronomer" or "astrologer" in Old English: tunglere, tungolcræftiga, tungolwītega, tīdymbwlātend, tīdscēawere. In Modern English, however, the role of such synonyms has largely been replaced in favour of equivalents taken from Latin, French, and Greek. Familiarity with the etymology of groups of synonyms can give English speakers greater control over their linguistic register. See: List of Germanic and Latinate equivalents in English, Doublet (linguistics).

An exception to this and a peculiarity perhaps unique to a handful of languages, English included, is that the nouns for meats are commonly different from, and unrelated to, those for the animals from which they are produced, the animal commonly having a Germanic name and the meat having a French-derived one. Examples include: deer and venison; cow and beef;swine/pig and pork; and sheep/lamb and mutton. This is assumed to be a result of the aftermath of the Norman conquest of England, where an Anglo-Norman-speaking elite were the consumers of the meat, produced by lower classes, which happened to be largely Anglo-Saxon, though this same duality can also be seen in other languages like French, which did not undergo such linguistic upheaval (e.g. boeuf "beef" vs. vache "cow"). With the exception of beef and pork, the distinction today is gradually becoming less and less pronounced (venison is commonly referred to simply as deer meat, mutton is lamb, and chicken is both the animal and the meat over the more traditional term poultry. (Use of the termmutton, however, remains, especially when referring to the meat of an older sheep, distinct from lamb; and poultry remains when referring to the meat of birds and fowls in general.)

There are Latinate words that are used in everyday speech. These words no longer appear Latinate and oftentimes have no Germanic equivalents. For instance, the words mountain,valley, river, aunt, uncle, move, use, 

push and stay ("to remain") are Latinate. Likewise, the inverse can occur: acknowledge, meaningful, understanding, mindful,  behaviour, forbearance,behoove, forestall, allay, rhyme, 

starvation, embodiment come from Anglo-Saxon, and allegiance, abandonment, debutant, feudalism, seizure, 

guarantee, disregard, wardrobe,disenfranchise, disarray, 

bandolier, bourgeoisie, debauchery, performance, furniture, 

gallantry are of Germanic origin, usually through the Germanic element in French, so it is oftentimes impossible to know the origin of a word based on its register.

English easily accepts technical terms into common usage and often imports new words and phrases. Examples of this phenomenon include contemporary words such as cookie, Internet and URL (technical terms), as well as genre, über, lingua franca and amigo (imported words/phrases from French, German, Italian, and Spanish, respectively). In addition, slang often provides new meanings for old words and phrases. In fact, this fluidity is so pronounced that a distinction often needs to be made between formal forms of English and contemporary usage.