In a manner that is somewhat like glee or joy; with a hint of mischievous delight.
From 'glee' (Old English 'glēo' meaning entertainment or music) plus the suffix '-ish' (making it partial or resembling) plus '-ly' (making it an adverb). The suffix chain creates a word meaning 'in a somewhat gleeful way.'
This word shows how English lets us stack suffixes like building blocks—glee becomes gleeish (somewhat gleeful), which becomes gleeishly (doing it in a somewhat gleeful way). Medieval entertainers called 'gleemen' used the same root word, so your joy comes from the same linguistic ancestor as ancient musicians!
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