concave area
21Quadrilateral — This article is about four sided mathematical shapes. For other uses, see Quadrilateral (disambiguation). Quadrilateral Six different types of quadrilaterals Edges and vertices 4 …
22optics — /op tiks/, n. (used with a sing. v.) the branch of physical science that deals with the properties and phenomena of both visible and invisible light and with vision. [1605 15; < ML optica < Gk optiká, n. use of neut. pl. of OPTIKÓS; see OPTIC,… …
23Polygon — For other uses, see Polygon (disambiguation). Some polygons of different kinds In geometry a polygon (   …
24Kite (geometry) — Kite A kite showing its equal sides and its inscribed circle. Type Quadrilateral Edges and vertices 4 Symmetry group D1 (*) In Euclid …
25photoreception — photoreceptive, adj. /foh toh ri sep sheuhn/, n. the physiological perception of light. [1905 10; PHOTO + RECEPTION] * * * Biological responses to stimulation by light, most often referring to the mechanism of vision. In one celled organisms such …
26valley — valleylike, adj. /val ee/, n., pl. valleys. 1. an elongated depression between uplands, hills, or mountains, esp. one following the course of a stream. 2. an extensive, more or less flat, and relatively low region drained by a great river system …
27telescope — /tel euh skohp /, n., adj., v., telescoped, telescoping. n. 1. an optical instrument for making distant objects appear larger and therefore nearer. One of the two principal forms (refracting telescope) consists essentially of an objective lens… …
28Dome — For other uses, see Dome (disambiguation). Domal redirects here. For domal consonants , see Retroflex consonant. Dome of St. Peter s Basilica in Rome crowned by a cupola. Designed primarily by Michelangelo, the dome was not completed until 1590 A …
29Mosque of Uqba — Great Mosque of Kairouan Overview of the mosque s courtyard which is surrounded by colonnaded arches Basic information Location …
30river — river1 riverless, adj. riverlike, adj. /riv euhr/, n. 1. a natural stream of water of fairly large size flowing in a definite course or channel or series of diverging and converging channels. 2. a similar stream of something other than water: a… …
