From the second edition (1989):
(ˈfriːbuːtə(r)) Also 6 frebetter, fribooter, 7 frybuter. [ad. Du. vrijbuiter (Kilian vrijbueter) = Ger. freibeuter, f. the equivalents of free a., booty or boot n.2, -er1. Cf. also Eng. flibutor, s.v. filibuster.]

One who goes about in search of plunder; esp. a pirate or piratical adventurer.

1570 Michael Coulweber in Burgon Life Gresham II. 360 For so much as I was spoyled by the waye in cominge towards England by the Duke of Alva his frebetters, maye it please the Queenes Majestie [etc.]. 1598 Hakluyt Voy. I. To Rdr. *5 They tooke fiue‥ships of the Freebooters. 1622 Malynes Anc. Law-Merch. 179 If the ship become assailed by Pirats or Frybuters. a1659 Bp. Brownrig Serm. (1674) I. xxix. 376 The Danites were‥Free-booters‥and did all by force. 1726 G. Shelvocke Voy. round World 12 The ships there‥fired several shot at me, mistaking me for a free Booter. 1776 Adam Smith W.N. iv. vii. (1869) II. 151 St. Domingo was established by pirates and free booters. 1838 Thirlwall Greece V. xlii. 214 Every freebooter was, or might easily become, a pirate. 1856 Olmsted Slave States 314 These rail-road freebooters.
transf. and fig. 1600 W. Watson Quodlibets Relig. & State iv. (1602) 100 So‥to send abroad his fribooters‥against other words and writings. a1656 Bp. Hall. Occas. Medit. (1851) 20 Those spiritual freebooters, that lie in wait for our souls. 1886 A. Winchell Walks & Talks Geol. Field 240 The fierce shark is the free-booter of the ocean.

Hence †ˈfreebooter v. intr. (see quot.); ˈfree-ˌbootery, the practice of freebooters.

1659 Torriano, Vivere à discrettione‥for a souldier to free-booter or free-quarter in any place. 1822 T. L. Peacock Maid Marian xviii. 273 In the pure principles of freebootery have they excelled all men. 1851 Sir F. Palgrave Norm. & Eng. I. 448 The Pirate-Kings‥agreed unanimously to forego their free-bootery.