hydro-, hydra-, hydr-, hyd-

(Greek: water)

hydroadipsia
The absence of thirst for water.
hydroanemophily
Thriving in water and wind; a reference to plants that discharge air-borne spores after getting wet and producing structures.
hydrobarometry
Measurement of the depths in the sea based on hydrostatic pressure.
hydrobiology
1. The study of life, or living organisms, in aquatic habitats.
2. The study of live forms in bodies of water; such as, lakes or estuaries.
hydrobiont
An organism living mainly in water.
hydrobios
The sum total of all aquatic life; that part of the earth’s surface occupied by aquatic organisms.
hydrobiosis
The development of living organisms, as bacteria, in fluid media; the conditions of life of such organisms; fluid media.
hydroblepharon
A watery swelling of the eyelid.
hydrocarpic
Aquatic plants having flowers which are fertilized out of the water but submerged for development of fruit.
hydrocele
An accumulation of serous fluid in a body cavity; especially, between the visceral and parietal layers of the tunica vaginalis in the scrotum.
hydrocelectomy
The surgical process of removing a hydrocele (the accumulation of fluid in the coat around the testis).

Small hydroceles tend to disappear by one year of age while larger hydroceles may persist and warrant surgery.

hydrocenosis (s) (noun), hydrocenoses (pl)
A procedure by which an abnormal serous fluid accumulation is drained from the body.
hydrocephalic
Describing, pertaining to, or affected by hydrocephalus.
hydrocephaloid
Resembling hydrocephalus because of an apparently enlarged cranium which is seen in some cases of starvation, but without any abnormal accumulation of cerebrospinal fluid.
hydrocephalus (s) (noun) (no plural)
1. A congenital condition in which an abnormal accumulation of fluid in the cerebral ventricles causes enlargement of the skull and compression of the brain, destroying much of the neural tissue: "Hydrocephalus is also known as 'water on the brain' and it may be of sudden onset (acute hydrocephalus) or be slowly progressive (chronic hydrocephalus."
2. An accumulation of serous fluid within the cranium: especially, in infancy, because of an obstruction of the movement of cerebrospinal fluid, often causing a significant enlargement of the head: "When a person has hydrocephalus, he or she has an abnormal prominence of the forehead, brain atrophy, with mental deterioration and convulsions."

Cross references of word families that refer to "water": aqua-; hydat-; hygro-.