- hebdomadal (adj.)
- 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.
- hebdomadally (adv.)
- "weekly," 1816, pedantic humor, from hebdomadal + -ly (2).