The word is still "in the books," but hardly ever heard in conversations today.
Failaye means "to betray." According to some old dictionaries, it can also mean "cunning, deceit" or a crime done with forethought, as in premeditated murder which would be "failaye pumuno'."
Some of the older dictionaries spell it failahye, with an H. In the photo above, of a document written in 1902, the H is missing, but, in those days, people spelled in a very inconsistent way. Since it's more usual to forget a letter than to put one in that doesn't belong, and since three very old dictionaries (1865, 1918 and 1932) all have the H, I reckon failahye is the more accurate spelling, matching the pronunciation of the word in those days.
Påle' Román (1932) says that failahye can be used to describe interrupted sleep. Hu failahye i maigo'-ho. All those interruptions, waking one up, is a betrayal of the desire to sleep long.
The fafailahye is the traitor and finailahye is the noun form for "treason, betrayal."
Failahye was replaced in conversation by the people themselves with the Spanish loan words traidot (traitor) and traiduti (to betray). Fa'baba is a Chamorro word than can mean "to betray," but it has a wider meaning, including "to fool, trick, cheat, pretend, defraud."
In 1902, there was a man named Antonio Blas who was nicknamed Antonio'n Failaye.
Failahye seems very close to the word fa'aila', which means "to accuse." Later, the word took on more meaning, such as "to report on." I wonder if there is a connection between failahye (to betray) and fa'aila' (to accuse). Even fa'aila' has been forgotten, most people saying sokne or akusa for "accuse." Sokne really means more than "to accuse," but that's a topic for a future post.