Neoclassical compounds are compound words composed from combining forms (which act as affixes or stems) derived from classical languages (classical Latin or ancient Greek) roots. Neo-Latin comprises many such words and is a substantial component of the technical and scientific lexicon of English and other languages, via international scientific vocabulary (ISV). For example, Greek bio- combines with -graphy to form biography ("life" + "writing/recording").

Neoclassical compounds represent a significant source of Neo-Latin vocabulary. Moreover, since these words are composed from classical languages whose prestige is or was respected throughout the Western European culture, these words typically appear in many different languages. Their widespread use makes technical writing generally accessible to readers who may only have a smattering of the language in which it appears.

Not all European languages have been equally receptive to neoclassical technical compounds. German and Russian, for instance, have historically attempted to create their own technical vocabularies from native elements. Usually, these creations are German and Russian calques on the international vocabulary, such as Wasserstoff and "водород" (vodoród) for hydrogen. Like any exercise in language prescription, this endeavour has been only partially successful, so while official German may still speak of a Fernsprecher, public telephones will be labelled with the internationally recognized Telefon.

These words are compounds formed from Latin and Ancient Greek root words. Ancient Greek words are almost invariably romanized (see transliteration of Ancient Greek into English). In English:

Thus, for example, Ancient Greek σφιγξ becomes English (and Latin) sphinx. Exceptions to these romanizing rules occur, such as leukemia (leukaemia); compare leukocyte, also leucocyte. In Latin, and in the target languages, the Greek vowels are given their neoclassical values rather than their contemporary values in demotic Greek.

Ancient Greek words often contain consonant clusters which are foreign to the phonology of contemporary English and other languages that incorporate these words into their lexicon: diphthong; pneumatology, phthisis. The traditional response in English is to treat the unfamiliar cluster as containing one or more silent letters and suppress their pronunciation, more modern speakers tend to try and pronounce the unusual cluster. This adds to the irregularities of English spelling; moreover, since many of these words are encountered in writing more often than they are heard spoken, it introduces uncertainty as to how to pronounce them when encountered.

Neoclassical compounds frequently vary their stressed syllable when suffixes are added: ágriculture, agricúltural. This also gives rise to uncertainty when these words are encountered in print. Once a classical compound has been created and borrowed, it typically becomes the foundation of a whole series of related words: e.g. astrology, astrological, astrologer/astrologist/astrologian, astrologism.

Mainstream medical and ISV pronunciation in English is not the same as Classical Latin pronunciation. Like Ecclesiastical Latin, it has a regularity of its own, and individual sounds can be mapped or compared. Although the Classical Latin pronunciation of venae cavae would be approximately /ˈwɛnaɪˈkɑːwaɪ/, the standard English medical pronunciation is /ˈviːniːˈkeɪviː/.