Mental retardation

Disorder characterized by significantly below average general intellectual function with deficits or impairments in the ability to learn and to adapt socially. The cause may be genetic, biological, psychosocial, or traumatic.

Mentor

Guide or teacher who offers advice, criticism, wisdom, guidance, and perspective to an inexperienced but promising protégé to help reach a life goal.

Mercantile risk

A term most often used in Property Insurance meaning a retail or wholesale risk as contrasted with a service risk, a manufacturing risk, or a habitational risk.
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Hazard or peril or a merchant in selling his stock of goods.