nychthemeral

• nycthemeral, nyctohemeral, nictemeral, nuchthemerinal

From nychthemeron +‎ -al.

• IPA^(key): /ˈnɪk.θɛm(ə)ɹəl/

nychthemeral (not comparable)

1. Relating to or lasting a nychthemeron (a period of 24 hours).
   • 1919, George Howard Parker, The Elementary Nervous System, Philadelphia: J. B. Lippincott & Co., →OCLC, page 163:

     Observations on sea-anemones in dimly lighted situations, such as under bridges and so forth, showed that these animals were more or less continuously expanded, but aside from such exceptions it was clear that Metridium in its natural surroundings exhibited a well-marked nychthemeral rhythm.

• hypernychthemeral

• circadian
• diurnal

• “nycthemeral, adj.”, in OED Online ⁠, Oxford, Oxfordshire: Oxford University Press, launched 2000.