Experienced sailor (6)
(Other definitions for seadog that I've seen before include "Mate, perhaps" , "Rating" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">experienced sailor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sea dog that I've seen before include "'Old salt (3,3)'" , "Old or experienced sailor" , "Dosage (anag)" , "Experienced sailor (colloq.)" , "mythical creature" .)