More about thusly :
Webster’s Second labels the word “colloquial.” Webster’s Third drops the label and adds a citation from the Congressional Record : “he summoned his counselors and spoke ∼ to them.”
The first and second editions of Fowler’s Modern English Usage make no reference to the word.
Bergen Evans and Cornelia Evans’s A Dictionary of Contemporary American Usage (1957) suggests that the word is “the product of illiteracy or exuberance.” The Evanses’ conclusion: “Thus is an adverb and nothing is gained by attaching the regular adverbial suffix -ly to it.”
Theodore Bernstein’s The Careful Writer (1965) calls the word a casualism, and a superfluous one: “it says nothing that thus does not say.”
Wilson Follett’s Modern American Usage: A Guide (1966) mentions the word in passing: “we add -ly for ridiculous or jocular effects to forms that are already adverbs: muchly , thusly .”
The Merriam-Webster Dictionary of English Usage (1989) makes a point missing from other discussions:
One reason thusly has gradually been able to gain a secure foothold in the language is undoubtedly that it is used primarily in ways that are, to some degree, distinct from the principal uses of thus .M-W points out that “thusly almost always follows the verb it modifies” and that “its most frequent use is as an introductory word preceeding a quotation or other passage set off by a colon.” Zounds! That’s just how I’ve used the word. For instance:
The American Heritage Dictionary . . . defines banausic thusly: &c.I knew I wasn’t being ridiculous or jocular.
The Magic Rub’s maker, Prismacolor, describes the eraser thusly: &c.
M-W is not my favorite usage guide: too often its advice seems to be to do what you like. But I like its advice about thusly :
[W]hatever its origins, thusly is not now merely an ignorant or comic substitute for thus : it is a distinct adverb that is used in a distinct way in standard speech and writing. Knowledge of the subtleties of its use may give you the courage to face down its critics, but if discretion, prudence, or faintheartedness compels you to shun it (or if you just dislike it), our advice is not to replace it automatically with thus but to consider instead a more natural-sounding phrase such as “in this way” or “as follows.”I’m not faint of heart: I’ve restored the two thusly s I’ve quoted above. The third remains gone, replaced by a plain, more suitable as :
Gevalia describes its Traditional Roast[Google’s Ngram Viewer shows thusly rising sharply since 1996.]