Wordnet 3.0
ADJECTIVE (2)
1. 
 of or relating to a coast; 
- Example: "coastal erosion"2. 
 located on or near or bordering on a coast; 
- Example: "coastal marshes"- Example: "coastal waters"- Example: "the Atlantic coastal plain"
The Collaborative International Dictionary of English v.0.48:
Coastal \Coast"al\, a.
   Of or pertaining to a coast.
   [1913 Webster]
WordNet (r) 3.0 (2006):
coastal
    adj 1: of or relating to a coast; "coastal erosion"
    2: located on or near or bordering on a coast; "coastal
       marshes"; "coastal waters"; "the Atlantic coastal plain"
       [ant: inland]
Moby Thesaurus II by Grady Ward, 1.0:
28 Moby Thesaurus words for "coastal":
   bordering, borderline, boundary, bounding, determinant,
   determinative, determining, extreme, fringing, frontier, limbic,
   liminal, limit, limiting, littoral, marginal, rimming, riparial,
   riparian, riparious, riverside, seaside, shore, shoreside,
   shoreward, skirting, terminal, threshold