1 a (usu. foll. by at) (of a line, arc, figure, etc.) form (an angle) at a particular point when its extremities are joined at that point. b (of an angle or chord) have bounding lines or points that meet or coincide with those of (a line or arc).
2 Bot. (of a bract etc.) extend under so as to embrace or enfold.
Etymology: L subtendere (as SUB-, tendere stretch)
Useful english dictionary. 2012.