dissoner

A rare, mostly musical/literary verb meaning to clash or sound discordant — the verbal counterpart of the adjective dissonant, essentially confined to music criticism and formal writing about clashing colors or ideas.

• Cet accord dissone étrangement dans la mélodie. — That chord sounds oddly discordant in the melody.
• Ses propos dissonent avec le ton du discours. — His remarks clash with the tone of the speech.
• Les couleurs choisies dissonent un peu. — The colors chosen clash a little.

This is a low-frequency, formal-register verb — détonner is the everyday word for "to clash/stick out," and most French speakers reach for that instead of dissoner in casual conversation.

Often confused with détonner.