branler

Literally to be loose or wobbly (une dent qui branle, a wobbly tooth), and in the fixed idiom branler dans le manche, to be shaky/unstable/precarious (an affair or a person not solid). Note: in vulgar slang, se branler means to masturbate — this sense is extremely common in casual speech and dominates the verb's register today, so use it carefully.

• Cette chaise branle, fais attention en t'asseyant. — This chair is wobbly, be careful sitting down.
• Son projet branle dans le manche depuis le début. — His project has been shaky from the start.
• Une de mes dents branle depuis hier. — One of my teeth has been loose since yesterday.

Because se branler is vulgar slang for masturbating, even the innocent literal senses (wobbly tooth, loose object) can sound risqué or trigger a snicker in casual conversation — bouger or être instable are safer, neutral alternatives outside a deliberately colloquial context.

• expression "Branler dans le manche" — A French idiom dating to the 17th century (preceded by branler au manche a century earlier), describing a tool head loose in its handle — extended since the 18th century to describe an unstable situation or an unreliable, wavering person.