Anatomy, a small plexus or network of vessels in the brain, surrounding the pituitary gland.

Retention is defined by Mr Locke to be, a faculty of the mind, whereby it keeps or retains those simple ideas it has once received, by sensation or reflection. See Metaphysics, Part I. Chap. ii.

Retention, is also used, in medicine, &c. for the state of contraction in the solids or vascular parts of the body, which makes them hold fast their proper contents. In this sense, retention is opposed to evacuation and excretion.