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THEMATIC VOWEL, also thematic. In an inflected language like Greek or Latin, the VOWEL which adheres to a root or base, to form its stem or theme. This vowel then usually controls the inflectional and derivational affixes attaching to it: for example, in the Latin verb amare (to love), the base is am, the thematic vowel -a-, and the STEM ama-. The vowel appears in all or most of the other inflected forms and derivatives of a thematic group; for the amare group (the first conjugation of Latin verbs), a appears throughout the imperfect tense: amabam, amabas, amabat, amabamus, amabatis, amabant. A selection of Latin words formed by means of thematic -i- is shown in the accompanying table.


Thematic vowel



aud (hear)



audio (I hear)


audiens (hearing)


auditor (hearer)

agr (field)



agricola (field-tender)


agricultura (field-tending)

hort (garden)



horticultura (garden-tending)

Thematic vowels from Greek and Latin are common in English, often serving to mark sets or families of words: (1) Latin, -a- as in dictate/dictator, negotiate/negotiator/negotiable, audacious/audacity, tenacious/tenacity; -e- as in complete/completion, convenient/convenience, Venus/venereal, larynx/laryngeal; -i- as in audit/audience/audition, agriculture/horticulture, minister/ministerial, president/presidential, space/spatial; -o- as in atrocious/atrocity, ferocious/ferocity; -u- as in residue/residual, use/usual, vacuous/vacuity, ambiguous/ambiguity, acupuncture/acupressure; -y/i- as in colony/colonial, Italy/Italian/Italianate, auditory/auditorium. (2) Greek, -a- as in dogma/dogmatism, theme/thematic; -e- as in frenzy/frenetic, phonetic/phonemic; -eu- as in hermeneutic/pharmaceutical; -i- as in arthritis/arthritic, basis/basic, crisis/critic/criticism; -o- as in astrophysics/astrophysicist, biography/biographical, hypnosis/hypnotic/hypnotism, neurosis/neurotic. See COMBINING FORM, INTERFIX.

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