bissextileBeing or having an intercalary day, particularly the quadrennial leap day of the Julian and Gregorian calendars traditionally placed as a "second sixth" day before March 1st.
biviumOne side of an echinoderm, including a pair of ambulacra, in distinction from the opposite side (trivium), which includes three ambulacra.
black bileOne of the four humours of ancient and mediaeval physiology, that was believed to be secreted by the kidneys and spleen and to cause melancholy and sadness when present in excess.
boleteA type of fruiting body produced by certain fungus species in the order Boletales, especially those of genus Boletus, many of which are prized for their flavour; any species of said order that produces such a fruiting body.
bombaxAny member of the genus Bombax of tropical trees in the mallow family.
bombic acidAn acid obtained from the silkworm, now found to be acetic acid.
bonus geniusA small wooden doll that is covered with a cape and made to vanish as part of a magic trick.
BoötesA circumpolar constellation of the northern sky, called the “bear-guard” or the “herdsman”. It includes the fourth-brightest star in the night sky, Arcturus.
bordageThe low-level tenure by which a bordar held his cottage.
bordarA person ranking below villeins and above serfs in the social hierarchy of a manor, holding just enough land to feed a family (about five acres) and required to provide labour on the demesne on specified days of the week.
brumationA lethargic state that some ectothermic animals, such as many reptiles, assume during cold conditions. Partly analogous to hibernation, but physiological differences include that brumation does not depend on stored fat, but rather on reduced metabolic activity.
BrunonianOf or relating to John Brown (physician, born 1735), Scottish physician who taught that disease was caused by either excessive or inadequate stimulation.
BruttiumA former district of southern Italy in the time of the Roman Empire.
bufoniteA fossil consisting of the petrified teeth and palatal bones of fishes belonging to the family of pycnodonts, whose remains occur in the oolite and chalk formations.
bulbus glandisAn erectile tissue structure on the penis of canid mammals and some pinnipeds, which swells up and locks inside the female during sexual intercourse.
bulimia nervosaAn eating disorder characterized by a binge-and-purge cycle: extreme overeating followed by self-induced vomiting.