aditus: Latin ad = to, towards, iter = a way, hence an opening or entrance.
adrenal: Latin ad = towards, at, ren = kidney, hence situated near the kidney (see suprarenal)
adrenergic: adjective, Latin ad = at, ren = kidney, and Greek ergon = work, hence, stimuli which cause the adrenal (suprarenal) gland to produce adrenaline. Used to specify neurons or pathways which use adrenaline as a transmitter.
afferent: adjective, Latin ad = to, and ferent = carrying (cf. ferry), hence, carrying to, e.g., axons carrying information from retina to lateral geniculate nucleus are afferents to that nucleus.
aponeurosis: Greek apo = from, and neuron = tendon (later applied to nerve cell and its fibres), used for sheet-like tendons. Adjective - aponeurotic.
apophysis: Greek apo = from, and physis = growth, hence, a bony process - reserved for the articular process of a vertebra; adjective - apophysial.
appendage: Latin appendere = to hang on, supplement.
appendix: Latin appendere = to hang on, supplement.
apposition: Latin appositus = placed at, hence, in contact, in juxtaposition.
aqueduct: Latin aqua = water, and ductus = drawn or led off, hence a channel for conducting fluid, e.g. the cerebral aqueduct of the midbrain, which transmits fluid from the 3rd to the 4th ventricle.
arachnoid: adjective, Greek arachne = spider, and eidos = shape or form, hence like a spiders web. This middle layer of the three meninges is spread web-like over the brain when the dura has been removed.
arbor vitae: Latin arbor = tree, and vita = life, hence, resembling the tree of life. This colourful term is used to describe the pattern of cerebellar folia seen in a median section.
archaeocerebellum: Greek archi = first, hence the oldest part of the cerebellum, which is the flocculonodular lobe.
archaeopallium: Greek archi = first, and pallium = cloak, hence the cortex which developed first in vertebrates. Often synonymous with hippocampal formation.
archicerebellum: Greek archi = first, hence the oldest part of the cerebellum, which is the flocculonodular lobe.
archipallium: Greek archi = first, and pallium = cloak, hence the cortex which developed first in vertebrates. Often synonymous with hippocampal formation.
archistriatum: Greek archi = first, and Latin striatum = streaked or fluted.
astrocyte: Greek astron = star, and kytos = cell, hence a star-shaped (neuroglial) cell.
ataxia,: Greek a = negative, and taxis = order, hence inability to co-ordinate the voluntary muscles.
atlas: Greek atlao = I sustain. Atlas was a mythical god who sustained the globe on his shoulders. The 1st vertebra sustains the skull, and its upper surface bears 2 concavities which suggest Atlas' palms, not shoulders.
atresia: Greek a = negative, and tresis = a hole, hence an absence or closure of a body orifice or tubular organ
atrium: Latin = entrance hall, adjective - atrial.
atrophy: Greek a = negative, and trophe = food, hence wasting from starvation.
auditory: Latin audire = to hear, hence, pertaining to the ear.