1) Nautical terminology 2) Sailboat component 
A boomkin, sometimes referred to as a bumkin or as a bumpkin, consists of an exceptionally strong and usually wooden spar that projects forwards and often (though not always) downwards over the main head-rail of a traditional western sailing ship, one on either side of the vessel (not to be confused with cathead). The heel of this spar is usually ...
• (n.) Same as Bumkin.
Moonkin druid
A spar projecting from the stern to which a backstay is attached.
Boom'kin noun (Nautical) Same as Bumkin . 
A spar projecting from the stern to which is attached a backstay or sheet. 
Short spar extending aft from the transom. Used to anchor the backstay or the sheets from the mizzen on a yawl or ketch.