focal

• POS: Adjective
• HYPHEN: fo=cal

CIDE DICTIONARY

focal, a. [Cf. F. focal. See Focus.].

 Belonging to,or concerning, a focus; as, a focal point.  [1913 Webster]

Focal distance, or length, of a lens or mirror (Opt.), the distance of the focus from the surface of the lens or mirror, or more exactly, in the case of a lens, from its optical center. --Focal distance of a telescope, the distance of the image of an object from the object glass.

OXFORD DICTIONARY

focal, adj. of, at, or in terms of a focus.

Idiom

focal distance (or length) the distance between the centre of a mirror or lens and its focus. focal plane the plane through the focus perpendicular to the axis of a mirror or lens. focal point = FOCUS n. 1.

Etymology

mod.L focalis (as FOCUS)

THESAURUS

focal

approaching, arch, asymptotic, banner, basic, bedrock, capital, cardinal, central, centralized, centred, centripetal, centrolineal, champion, chief, concentrated, concurrent, confluent, confocal, connivent, convergent, converging, crowning, dominant, essential, first, foremost, fundamental, great, headmost, hegemonic, indispensable, leading, life-and-death, life-or-death, magisterial, main, master, material, meeting, mutually approaching, of vital importance, overruling, paramount, predominant, preeminent, preponderant, prevailing, primal, primary, prime, principal, radial, radiating, ranking, ruling, sovereign, star, stellar, substantive, supereminent, tangent, tangential, topflight, uniting, vital

ROGET THESAURUS

focal

Centrality

N centrality, centricalness, center, middle, focus, core, kernel, nucleus, nucleolus, heart, pole axis, bull's eye, nave, navel, umbilicus, backbone, marrow, pith, vertebra, vertebral column, hotbed, concentration, centralization, symmetry, center of gravity, center of pressure, center of percussion, center of oscillation, center of buoyancy, metacenter, central, centrical, middle, azygous, axial, focal, umbilical, concentric, middlemost, rachidian, spinal, vertebral, middle, midst, centrally.