vt. 对

[ verb ]
be opposite to; of angles and sides, in geometry
<verb.stative> delimit

Subtend \Sub*tend"\, v. t. [imp. & p. p. {Subtended}; p. pr. &
vb. n. {Subtending}.] [L. subtendere; sub under + tendere to
stretch, extend. See {Tend}.]
To extend under, or be opposed to; as, the line of a triangle
which subtends the right angle; the chord subtends an arc.