This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Biology Relating to or exhibiting approximately 24-hour periodicity.

adj. of, relating to, or showing rhythmic behaviour with a period of 24 hours; especially of a biological process

adj. of or relating to biological processes occurring at 24-hour intervals

"The term circadian rhythms refers to biological cycles that repeat about every twenty-four hours."

infradian    ultradian   

circadian rhythm   

Akkadian    Arcadian    Canadian    Chadian    arcadian    canadian   

negative-feedback    redox    copper-containing    microsomal    day-night    autocrine    cyanobacterial    transcriptional    fibrinolytic    hardest.those