The Collaborative International Dictionary of English v.0.48:

Seafaring \Sea"far`ing\, a.
   Following the business of a mariner; as, a seafaring man.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seafaring
    adj 1: used on the high seas; "seafaring vessels" [syn:
           oceangoing, seafaring, seagoing]
    n 1: the work of a sailor [syn: seafaring, navigation,
         sailing]
    2: travel by water [syn: water travel, seafaring]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "seafaring":
   boating, canoeing, circumnavigation, coasting, cruising,
   gunkholing, marine, maritime, motorboating, nautical, naval,
   navigability, navigating, navigation, navigational, ocean-going,
   oceanic, passage-making, pelagic, periplus, rowing, sailing, salty,
   sculling, sea travel, seamanlike, seamanly, steaming,
   travel by water, voyaging, water travel, water-borne, yachting