Etymology
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tacho- 

word-forming element meaning "speed," from Latinized form of Greek takho-, combining form of takhos "speed, swiftness, fleetness, velocity," related to takhys "swift," of unknown origin.

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tachy- 

word-forming element meaning "rapid, swift, fast," from Latinized combining form of Greek takhys "swift, rapid, hasty," related to takhos "speed, swiftness," of uncertain origin.

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-teen 

word-forming element making cardinal numbers from 13 to 19, meaning "ten more than," from Old English -tene, -tiene, from Proto-Germanic *tekhuniz (cognates: Old Saxon -tein, Dutch -tien, Old High German -zehan, German -zehn, Gothic -taihun), an inflected form of the root of ten; cognate with Latin -decim (source of Italian -dici, Spanish -ce, French -ze).

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-teenth 

word-forming element making ordinal numbers from 13 to 19, from -teen + -th (1), displacing Old English -teoða, -teoðe (West Saxon), related to teogoða (Anglian) "tenth."

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terato- 

before vowels terat-, word-forming element meaning "marvel, monster," from combining form of Greek teras (genitive teratos) "marvel, sign, wonder, monster," from PIE *kewr-es-, from root *kwer- "to make, form" (source also of Sanskrit krta- "make, do, perform," Lithuanian keras "charm," Old Church Slavonic čaru "charm").

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-th (1)

word-forming element making ordinal numbers (fourth, tenth, etc.), Old English -ða, from Proto-Germanic *-tha- (cognates: Gothic -da, -ta, Old High German -do, -to, Old Norse -di, -ti), from PIE *-to-, also *-eto-, *-oto-, suffix forming adjectives "marking the accomplishment of the notion of the base" [Watkins].

Cognate with Sanskrit thah, Greek -tos, Latin -tus; Sanskrit ta-, Lithuanian and Old Church Slavonic to, Greek to "the," Latin talis "such;" Greek tēlikos "so old, of such an age," Old Church Slavonic toli "so, to such a degree," toliku "so much," Russian toliko "only;" also see -ed.

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-th (2)

suffix forming nouns of action, state, or quality from verbs or adjectives (such as depth, strength, truth), from Old English -ðu, , from Proto-Germanic *-itho (cognates: Old Norse , Old High German -ida, Gothic -iþa), abstract noun suffix, from PIE *-ita (cognates: Sanskrit -tati-; Greek -tet-; Latin -tati-, as in libertatem "liberty" from liber "free"). Sometimes in English reduced to -t, especially after -h- (as in height).

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-theism 

word-forming element meaning "belief (of a specified kind) in God, a god, or gods," from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + -ism.

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-tion 

syllable formed when the word-forming element -ion (from Latin -io) is fixed to a base or to another suffix ending in -t or -te. In Middle English, in words via Old French, it often was -cion (in coercion and suspicion, however, the -c- belongs to the base).

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-tomy 

word-forming element meaning "a cutting" (especially a surgical incision or removal), from Greek -tomia "a cutting of," from tome "a cutting, section" (from PIE root *tem- "to cut").

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