person's name
鋮 is a rare kanji used primarily in personal names. Its standalone meaning is unclear beyond that name usage.
鋮 combines 金 (metal) with 成, which likely contributes the sound. The exact historical development is uncertain, and the character is rare.
The metal radical 金 suggests something metallic, and 成 can mean 'become' or 'achieve'. Picture a name engraved on a metal plate, becoming a permanent record.
For セイ, imagine a person named セイ receiving a metal award: say -> セイ, and the metal plate bears their name.