Past tense of 'fun' when used as a verb, though this usage is relatively rare and informal in modern English.
From 'fun' as a verb plus the regular past tense ending -ed, though 'fun' is more commonly used as a noun or adjective than as a verb in contemporary usage.
The word 'fun' has only recently become commonly used as a verb (like 'we funned around')—it's one of the ways modern English keeps evolving as speakers use familiar words in new ways!
Complete word intelligence in one call. Free tier — 50 lookups/day.