circadian
adjective /sɜːˈkeɪdiən/
  /sɜːrˈkeɪdiən/
[only before noun] (specialist)- connected with the changes in the bodies of people or animals over each period of 24 hours
- Jet lag occurs because jet travel ignores the circadian timekeeper.
 
Oxford Collocations DictionaryCircadian is used with these nouns:- clock
 - rhythm
 
Word Origin1950s: formed irregularly from Latin circa ‘about’ + dies ‘day’.