hebdomadal (adj.)youdaoicibaDictYouDict[hebdomadal 词源字典]
1610s, from Latin hebdomadalis, from hebdomas, from Greek hebdomas "the number seven; a period of seven (days)," from hepta "seven" (from PIE *septm; see seven) + -mos, suffix used to form ordinal numbers, cognate with Latin -mus. In later use as pedantic humor.[hebdomadal etymology, hebdomadal origin, 英语词源]
-teenthyoudaoicibaDictYouDict
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."
-th (1)youdaoicibaDictYouDict
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 telikos "so old," Old Church Slavonic toli "so," toliku "so much," Russian toliko "only;" also see -ed.