a. [ L. cohaerens, p. pr. See Cohere. ] 1. Sticking together; cleaving; as the parts of bodies; solid or fluid. Arbuthnot. [ 1913 Webster ]

2. Composed of mutually dependent parts; making a logical whole; consistent; as, a coherent plan, argument, or discourse. [ 1913 Webster ]

3. Logically consistent; -- applied to persons; as, a coherent thinker. Watts. [ 1913 Webster ]

4. Suitable or suited; adapted; accordant. [ Obs. ] [ 1913 Webster ]

Instruct my daughter how she shall persever,
That time and place, with this deceit so lawful,
May prove coherent. Shak. [ 1913 Webster ]

5. (Physics, Optics) Of or pertaining to electromagnetic waves that have a constant phase relationship with each other; having identical phase at all points; as, the coherent light produced by a laser. [ PJC ]

n. (Physics, Optics) Light in which the phases of all electromagnetic waves at each point on a line normal to the direction of the the beam are identical. Coherent light is usually monochromatic, and the most common source of such light for practical uses is from a laser. The constant phase relations of coherent light allows the achievement of certain effects, such as holography, not possible with noncoherent light. The low degree of angular dispersion of coherent light beams also allows the use of such light in laser ranging, over distances as far as from the earth to the moon. [ PJC ]

adv. In a coherent manner. [ 1913 Webster ]