TREASONABLY
faithlessly, traitorously, treacherously, treasonably, false
(adverb) in a disloyal and faithless manner; “he behaved treacherously”; “his wife played him false”
Source: WordNet® 3.1
Etymology
Adverb
treasonably (comparative more treasonably, superlative most treasonably)
In a treasonable manner.
Synonyms
• (in a treasonable manner): treasonously
Source: Wiktionary
TREASONABLE
Trea"son*a*ble, a.
Definition: Pertaining to treason; consisting of treason; involving the
crime of treason, or partaking of its guilt.
Most men's heads had been intoxicated with imaginations of plots and
treasonable practices. Clarendon.
Syn.
– Treacherous; traitorous; perfidious; insidious. --
Trea"son*a*ble*ness, n.
– Trea"son*a*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition