In a bootless manner; without success, uselessly, or to no avail; without achieving the desired result.
From 'bootless' (without benefit or success) plus '-ly' adverb suffix, creating an adverb form.
Adding '-ly' to turn adjectives into adverbs is so automatic in English that we often don't realize we're doing it—'bootlessly' sounds archaic and poetic, but it follows the exact same rule that creates 'quickly,' 'sadly,' and 'amazingly.'
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