tela: Latin = a web; e.g., a fold of pia mater containing a choroid plexus.
telencephalon: Greek telos = end, and enkephalos = brain; hence the rostral part of the developing brain. (With the diencephalon, it makes up the prosencephalon).
temporal: Latin tempus = time; hence, the temporal area of the scalp, where grey hair first appears, marking the progress of ageing.
testicle: Latin testiculus = the male gonad (see testis).
testis: Latin testiculus = the male gonad. From Latin testis = a witness. Under Roman law, no man could bear witness (testify) unless he possessed both testes. Plural - testes.
tetralogy: Greek tetra = four, and logos = discourse, hence a combination of four elements e.g., symptoms or defects.
tetrology: Greek tetra = four, and logos = discourse, hence a combination of four elements or symptoms.
thalamus: Greek = bedroom - derivation obscure, though the posterior end of the thalamus is rounded and named pulvinar = cushion.
trapezium: Greek trapezion = a trapezium - a quadrilateral with 2 sides parallel.
trapezius: Greek trapezion = a trapezium - a quadrilateral with 2 sides parallel; hence, trapezius muscle, the diamond-shape of both trapezii muscles together.
trapezoid: Greek trapezion = a trapezium - a quadrilateral with 2 sides parallel, and eidos = shape or form, hence resembling a trapezium.
triceps: Latin tres = 3, and caput = head; hence a 3-headed muscle.
trigeminal: Latin trigeminus = triplets; hence, cranial nerve V, with 3 large divisions.