R ˈapə(r)ˌchu̇(ə)r, -_chər; -R -pəˌchu̇ə, -pəchə noun
( -s )
Etymology: Middle English, from Latin apertura, from apertus open (from past participle of aperire to open, uncover, probably from ap- — akin to Latin ab from — + — assumed — verire to cover) + -ura -ure — more at of , weir
1. obsolete : the act or process of opening
2. : an opening or open space (as between parts or sections of solid matter) : hole , gap , cleft , chasm , slit
the only light … came through the narrow aperture between the stone lips — Willa Cather
3.
a. : an opening that restricts a beam of radiation or a stream of particles ; specifically : the opening in a photographic lens that admits the light passing through, the size often being controlled by an iris diaphragm
b. : the diameter of the entrance pupil of an optical system
4. : the opening of a univalve shell