Etymology: irregularly < Greek ἑπτά seven + -alsuffix1.Previous versions of the OED give the stress as: ˈheptal.
= hebdomadaln.
ΚΠ
1853 R. DunglisonMed. Lexicon (ed. 9) Cycle, Hebdomadal or Heptal. A period of seven days or years, which according to some, either in its multiple or submultiple, governs an immense number of phenomena of animal life.
This entry has not yet been fully updated (first published 1898; most recently modified version published online June 2019).