In a strange, wild, or unconventional manner; in a way that is freaky or unusual.
From 'freaky' plus the adverb-forming suffix '-ly' (Old English '-lice', from 'lic' meaning like or body). The suffix transforms adjectives into descriptions of how actions are performed.
The '-ly' suffix is one of English's most productive tools—we can add it to almost any adjective to describe how something happens, which is why 'freakily' feels natural even though 'freak' is brand new to English historically.
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