Of a person's memory: Not long retaining anything.

Of memory: Not retentive; forgetful.

Having or demonstrating an inability to hold, grasp, or embrace.

Liable or prone to slip; readily giving way. Also of the memory, forgetful.

figurative. Of persons, their tongues: Not reticent, blabbing. Of memory: Not retentive.

Not retentive; lacking the power of retention.

Not retentive (in various senses).