Definition of "flanker"

About two hours...they had been about the house before they prevailed to fire it (which they did with Flax and Hemp, which they brought out of the Barn, and there being no defence about the House, only two Flankers at two opposite corners and one of them not finished) they fired it once and one ventured out and quenched it, but they quickly fired it again, and that took.

1675, The Captivity of Mary Rowlandson, from The Portable Native American Indian Reader, New York: Penguin Books, 1977, page 312

[The planters’ houses] were frequently constructed with flankers and loopholes, for the purpose of firing upon the assailants when they approached so near.

1803, Robert Charles Dallas, The History of the Maroons‎, London: Longman and Rees, Volume 1, Letter 2, p. 27

It was in vain they threw out flankers, and endeavored to dislodge their assailants; each pause gave time for other pursuers to come within reach, and open attacks from different quarters.

1855, Washington Irving, chapter 37, in The Life of George Washington‎, volume 1, New York: Thomas Y. Crowell, page 278

the Castle was neither ſo weakly mann'd nor flanker'd as they were made belive

1634, T[homas] H[erbert], A Relation of Some Yeares Travaile, Begunne Anno 1626. into Afrique and the Greater Asia, […], London: […] William Stansby, and Jacob Bloome

[…] to my observation in our Climates, where those sharp winds do rather flanker than blow fully opposite upon our Plantations, they thrive best […]

1670, John Evelyn, Sylva or, A Discourse of Forest-Trees, and the Propagation of Timber in His Majesties Dominions, London, Chapter 3, “Of the Oak,” p. 19