In a crawling manner; moving slowly and close to the ground, or proceeding at an agonizingly slow pace.
From 'crawl' + '-ing' (present participle) + '-ly' (adverb suffix from Old English 'lice'). Each suffix layer adds grammatical meaning, building the adverbial form.
Notice how '-ly' transforms almost any adjective into an adverb—this suffix is one of English's most productive, used thousands of times in modern English every single day!
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