Wordnet 3.0
NOUN (1)
1. 
 an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator; 
- Example: "all points on the same meridian have the same longitude"[syn: meridian, line of longitude]
WordNet (r) 3.0 (2006):
line of longitude
    n 1: an imaginary great circle on the surface of the earth
         passing through the north and south poles at right angles
         to the equator; "all points on the same meridian have the
         same longitude" [syn: meridian, line of longitude]