bosar

A rare, archaic verb meaning to overflow or brim over — used for a liquid rising past a container's edge. Essentially obsolete in modern Spanish; you're very unlikely to encounter it outside old or highly regional texts.

• El agua bosaba por los bordes del cántaro. — The water was overflowing over the edges of the jug.
• El río bosaba tras la tormenta. — The river overflowed after the storm.
• En el texto antiguo se dice que el pozo bosaba de tanta lluvia. — In the old text, it says the well overflowed from so much rain.

This word is so rare that there's no real modern mistake to flag — rebosar or desbordar are what a learner should use for 'to overflow' today.

Often confused with rebosar.