To perceive (someone or something) as having a lower value, quantity, worth, etc., than what he/she/it actually has.
An estimate that is too low.
To believe, to think one grasps sufficiently despite potentially incomplete knowledge.
To stand underneath, to support.
To grasp a concept fully in one's mind, especially (of words, statements, art, etc.) to be aware of the meaning of and (of people) to be aware of the intent of.