Douglas Harper's Etymology Dictionary
Wiktionary
n. 1 (context biology English) Any cyclic biological or physiological pattern or activity 2 (context pseudoscience English) Any of three sinusoidal graphs, normally plotted by computer, having a person's birthdate as origin, that that are supposed to give meaningful information about emotional levels, physical energy levels, and mental/psychic sensitivity.
Wikipedia
A biorhythm (from Greek βίος - bios, "life" and ῥυθμός - rhuthmos, "any regular recurring motion, rhythm") is an attempt to predict various aspects of a person's life through simple mathematical cycles. Most scientists believe that the idea has no more predictive power than chance and consider the concept an example of pseudoscience.
Usage examples of "biorhythm".
Above the waistband, the lower set of eyesthe lensless ones that sent biorhythm signals to the structures that corresponded to the pineal gland in the human midbrainhad gone milky, signifying a new stage of endocrine changes.
New Amazonian day was inconvenient for creatures whose biorhythms were geared toward a twenty-four-hour cycle.
Above the waistband, the lower set of eyesthe lensless ones that sent biorhythm signals to the structures that corresponded to the pineal gland in the human midbrainhad gone milky, signifying a new stage of endocrine changes.
Each of us has a distinctive biorhythm, with peaks of energy at certain hours and valleys of fatigue between them.
As it turned out, he had told the officer that the hat was equipped with a biorhythm meter to help promote an even golf swing.
You ever go to a mall or an amusement park and see one of those machines where you drop in a quarter and it gives you your biorhythms, or your emotional state, or something like that?
Ever since they'd arrived at Zanthus he'd been on the verge, time stretched up here, knocking biorhythms along with the rest of normality.
Because they were native Atlanteans, with their biorhythms linked by the central computer to their current accounts, their short spell on deposit meant that each of them came out of the vault not only many stones heavier but many millions of dollars richer.
The four apprentices seemed to be adjusting the quickest to the stressfully unnatural biorhythms of habitat life and the bewildering amount of strange and new technology surrounding them.