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Webster 1913 Edition

(-sŭn)

Noun.

(Shipbuilding)

(a)

One of the triangular platforms in front of, and abaft, the paddle boxes of a steamboat.

(b)

One of the slanting supports under the guards of a steamboat.

(c)

One of the armored projections fitted with gun ports, used on modern war vessels.

sponson ‎(plural sponsons)

A projection from the side of a watercraft.
- 1907, Robert W[illiam] Chambers, “chapter IX”, in The Younger Set (Project Gutenberg; EBook #14852), New York, N.Y.: A. L. Burt Company, published 1 February 2005 (Project Gutenberg version), OCLC 4241346:
  
  He and Gerald usually challenged the rollers in a sponson canoe when Gerald was there for the weekend; or, when Lansing came down, the two took long swims seaward or cruised about in Gerald's dory, clad in their swimming-suits ; and Selwyn's youth became renewed in a manner almost ridiculous, […].