Whereas one might “86” an unneeded internal memo, one would “deep-six” an incriminating one. The term may have derived from navigation in earlier centuries, where anything more than 6 fathoms (36 feet / 11m) deep under water was unlikely to be recovered. Alternatively, this term could relate to burial at sea - that 6 fathoms was the legal minimum depth for the body to be immersed. |