An archaic or poetic form meaning 'ever' or 'eternally,' now mainly seen in proper names.
From 'ever' plus the adverbial suffix -ly. This formation became obsolete as -ly adverbs evolved, but it persists in surnames and place names like 'Everly' (as in The Everly Brothers).
The Everly Brothers' name looks like a surname but it's actually a forgotten adverbial form—their father chose it as a poetic name, unknowingly reviving a word that regular speakers had abandoned centuries earlier.
Complete word intelligence in one call. Free tier — 50 lookups/day.