noun
unnecessary addition; gilding the lily
A yojijukugo meaning to ruin something by adding an unnecessary extra touch, from a Chinese fable about drawing a snake and adding legs. Used to criticize superfluous improvements.
彼の提案は画蛇添足だ。
His suggestion is an unnecessary addition.
この説明は画蛇添足で、かえってわかりにくくなっている。
This explanation is gilding the lily and actually makes it harder to understand.
蛇足 is a shorter, more common synonym meaning 'redundancy' or 'superfluity', derived from the same story. 画蛇添足 is the full four-character idiom and is more emphatic.
From the Chinese fable 'Drawing a Snake and Adding Legs' (画蛇添足), where a man lost a contest by adding legs to his snake drawing, symbolizing unnecessary additions that spoil the original.