n. [ F., fr. L. horizon, fr. Gr. &unr_; (sc. &unr_;) the bounding line, horizon, fr. &unr_; to bound, fr. &unr_; boundary, limit. ] 1. The line which bounds that part of the earth's surface visible to a spectator from a given point; the apparent junction of the earth and sky. [ 1913 Webster ]

And when the morning sun shall raise his car
Above the border of this horizon. Shak. [ 1913 Webster ]

All the horizon round
Invested with bright rays. Milton. [ 1913 Webster ]

2. (Astron.) (a) A plane passing through the eye of the spectator and at right angles to the vertical at a given place; a plane tangent to the earth's surface at that place; called distinctively the sensible horizon. (b) A plane parallel to the sensible horizon of a place, and passing through the earth's center; -- called also rational horizon or celestial horizon. (c) (Naut.) The unbroken line separating sky and water, as seen by an eye at a given elevation, no land being visible. [ 1913 Webster ]

3. (Geol.) The epoch or time during which a deposit was made. [ 1913 Webster ]

The strata all over the earth, which were formed at the same time, are said to belong to the same geological horizon. Le Conte. [ 1913 Webster ]

4. (Painting) The chief horizontal line in a picture of any sort, which determines in the picture the height of the eye of the spectator; in an extended landscape, the representation of the natural horizon corresponds with this line. [ 1913 Webster ]

5. The limit of a person's range of perception, capabilities, or experience; as, children raised in the inner city have limited horizons. [ PJC ]

6. [ fig. ] A boundary point or line, or a time point, beyond which new knowledge or experiences may be found; as, more powerful computers are just over the horizon. [ PJC ]

Apparent horizon. See under Apparent. --
Artificial horizon, a level mirror, as the surface of mercury in a shallow vessel, or a plane reflector adjusted to the true level artificially; -- used chiefly with the sextant for observing the double altitude of a celestial body. --
Celestial horizon. (Astron.) See def. 2, above. --
Dip of the horizon (Astron.), the vertical angle between the sensible horizon and a line to the visible horizon, the latter always being below the former. --
Rational horizon, and
Sensible horizon. (Astron.) See def. 2, above. --
Visible horizon. See definitions 1 and 2, above. [ 1913 Webster ]

a. [ Cf. F. horizontal. ] 1. Pertaining to, or near, the horizon. “Horizontal misty air.” Milton. [ 1913 Webster ]

2. Parallel to the horizon; on a level; as, a horizontalline or surface. [ 1913 Webster ]

3. Measured or contained in a plane of the horizon; as, horizontal distance. [ 1913 Webster ]

Horizontal drill, a drilling machine having a horizontal drill spindle. --
Horizontal engine, one the piston of which works horizontally. --
Horizontal fire (Mil.), the fire of ordnance and small arms at point-blank range or at low angles of elevation. --
Horizontal force (Physics), the horizontal component of the earth's magnetic force. --
Horizontal line (Descriptive Geometry & Drawing), a constructive line, either drawn or imagined, which passes through the point of sight, and is the chief line in the projection upon which all verticals are fixed, and upon which all vanishing points are found. --
Horizontal parallax. See under Parallax. --
Horizontal plane (Descriptive Geometry), a plane parallel to the horizon, upon which it is assumed that objects are projected. See Projection. It is upon the horizontal plane that the ground plan of the buildings is supposed to be drawn. --
Horizontal projection, a projection made on a plane parallel to the horizon. --
Horizontal range (Gunnery), the distance in a horizontal plane to which a gun will throw a projectile. --
Horizontal water wheel, a water wheel in which the axis is vertical, the buckets or floats revolving in a horizontal plane, as in most turbines. [ 1913 Webster ]

n. [ Cf. F. horizontalité. ] The state or quality of being horizontal. Kirwan. [ 1913 Webster ]

adv. In a horizontal direction or position; on a level; as, moving horizontally. [ 1913 Webster ]