plancher

plancher (floor made of wood); floor (the interior bottom or surface of a house or building; the supporting surface of a room); floor (the bottom surface of a natural structure, entity, or space); lower limit

“débarrasser le plancher”

From planche + -er.

to study something thoroughly, to work hard on something, to brainstorm

“J'ai planché sur le sujet.” — I have made extensive research on the topic.

From planche + -er. Compare bûcher.