·adj Large; considerable.
II. Spanking ·p.pr. & ·vb.n. of Spank.
III. Spanking ·adj Moving with a quick, lively pace, or capable of so doing; dashing.
Large. ...
Dictionary of The Vulgar Tongue by Francis Grose
Going along with a fresh breeze when the spanker tells, as the aft well-boomed out-sail. The word is...
The Sailor's Word-Book
·- a strong breeze. ...
Webster's Dictionary of the English Language