This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
笟 combines 竹 (bamboo) and 瓜 (melon). The exact historical development is uncertain, but it likely originally referred to a bamboo tool or object related to gourds.
Bamboo 竹 over a melon 瓜: imagine a bamboo hoop or ring used to bind a melon or barrel. This shape may relate to the kun reading たが (hoop).
For コ, picture a bamboo hoop around a melon, and think of a child saying 'co-co' while tapping it: コ.