subtend

(transitive) To use an angle to delimit (mark off, enclose) part of a straight or curved line, for example an arc or the opposite side of a triangle.
(also, transitive) To extend or stretch opposite something; to be part of a straight or curved line that is opposite to and delimits an angle.
(transitive) To form the central angle of a circle underneath an arc.
(transitive) To stand beneath or close to, as a bract at the base of a flower.

Pronounced as (IPA)

/sʌbˈtɛnd/

From Latin subtendere, from sub (“under”) + tendere (“to stretch, extend”), itself a semantic loan from Ancient Greek ὑποτείνω (hupoteínō, “to subtend”), from which hypotenuse also derives. See tend.