The distance from one point on a wave (frequently shaped like a sine curve) to the next point in the same phase; i.e., from peak to peak or from trough to trough.
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wave·length -.leŋ(k)th n the distance in the line of advance of a wave from any one point to the next point of corresponding phase symbol lambda
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wave·length (λ) (wāvґlength) the distance between the top of one wave and the identical phase of the succeeding one.Medical dictionary. 2011.