The Collaborative International Dictionary of English v.0.48:

Southeast \South`east"\ (?; by sailors sou"-), n.
   The point of the compass equally distant from the south and
   the east; the southeast part or region.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Southeast \South`east\ (?; by sailors sou"-), a.
   Of or pertaining to the southeast; proceeding toward, or
   coming from, the southeast; as, a southeast course; a
   southeast wind.
   [1913 Webster]

WordNet (r) 3.0 (2006):

southeast
    adv 1: to, toward, or in the southeast [syn: southeast,
           south-east, sou'-east]
    adj 1: coming from the southeast; "southeasterly breezes" [syn:
           southeasterly, southeast]
    2: situated in or oriented toward the southeast [syn:
       southeast, southeastern, southeasterly]
    n 1: the compass point midway between south and east; at 135
         degrees [syn: southeast, sou'-east, southeastward,
         SE]
    2: the southeastern region of the United States [syn:
       Southeast, southeastern United States]
    3: the direction corresponding to the southeastward compass
       point
    4: a location in the southeastern part of a country, region, or
       city

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "southeast":
   Dixie, Dixieland, Down East, East, East Coast, Middle Atlantic,
   Middle West, New England, North, North Central region, Northeast,
   Northwest, Pacific Northwest, SE, SE by E, SE by S, SSE, South,
   Southeast, Southwest, Sunbelt, West, West Coast, Yankeeland,
   antarctic, arctic, austral, boreal, cardinal points, compass card,
   compass rose, degrees, east, eastbound, easterly, eastermost,
   eastern, easternmost, eastland, eastward, half points, hyperborean,
   lubber line, meridional, north, northbound, northeast,
   northeasterly, northeastern, northerly, northern, northernmost,
   northland, northward, northwest, northwesterly, northwestern,
   occident, occidental, orient, oriental, quarter points, rhumb,
   south, south-southeast, southbound, southeast by east,
   southeast by south, southeasterly, southeastern, southeastward,
   southeastwardly, southeastwards, southerly, southern, southernmost,
   southward, southwest, southwesterly, southwestern, sunrise, sunset,
   the Coast, west, westbound, westerly, western, westernmost,
   westland, westward, wild West