Definition of "subtend"

subtend

/sʌbˈtɛnd/

verb
third-person singular simple present subtends, present participle subtending, simple past and past participle subtended
1. (transitive, mathematics) 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.
2. (transitive, also mathematics) To extend or stretch opposite something; to be part of a straight or curved line that is opposite to and delimits an angle.
  Quotations
  ...trillions of bacteria, each equally an individual, which are found in a person’s gut, his mouth, his scalp, his skin and all of the crevices and orifices that subtend from his body’s surface.
  2012 August 16, “Me, myself, us”, in The Economist, issue
3. (transitive, mathematics) To form the central angle of a circle underneath an arc