In a chilly manner; with cold temperature, or in an unfriendly or unwelcoming way.
From 'chilly' plus the adverb-forming suffix '-ly.' Follows standard English patterns for converting adjectives to adverbs.
Adding '-ly' to adjectives to make adverbs is one of English's most productive patterns—you can probably guess what 'chillily' means even if you've never heard it before! That's the power of predictable word structure.
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