Adverb
in a disloyal and faithless manner
Source: WordNetThou hast most traitorously corrupted the youth of the realm in erecting a grammar-school; and whereas, before, our forefathers had no other books but the score and the tally, thou hast caused printing to be used; and, contrary to the king, his crown, and dignity, thou hast built a paper-mill. William Shakespeare
Thou hast most traitorously corrupted the youth of the realm in erecting a grammar school. William Shakespeare
he behaved treacherously Source: Internet
his wife played him false Source: Internet