ap·er·ture 
(ăpər-chər)
(ăpər-chər)n.
1. An opening, such as a hole, gap, or slit.
2.
a. A usually adjustable opening in an optical instrument, such as a camera or telescope, that limits the amount of light passing through a lens or onto a mirror.
b. The diameter of such an opening, often expressed as an f-number.
c. The diameter of the objective of a telescope.
[Middle English, from Latin apertūra, from apertus, past participle of aperīre, to open; see wer-4 in the Appendix of Indo-European roots.]
aper·tur′al adj.
- Indo-European root: nekw-t-
- Indo-European root: nem-
- Indo-European root: nepōt-
- Indo-European root: ner-
- Indo-European root: ner-
- Indo-European root: nes-
- Indo-European root: nes-
- Indo-European root: neu-
- Indo-European root: newn̥
- Indo-European root: newo-
- Indo-European root: nobh-
- Indo-European root: nogh-
- Indo-European root: nogw-
- Indo-European root: nu-
- Indo-European root: nāu-
- Indo-European root: nō̆-men-
- Indo-European root: n̥dher-
- Indo-European root: od-
- Indo-European root: oi-no-
- Indo-European root: oit-
- Indo-European root: oktō(u)
- Indo-European root: okw-
- Indo-European root: op-
- Indo-European root: or-
- Indo-European root: orbh-