‘Having the power to enter far into a subject’ (Johnson), penetrating, profound; having profound knowledge, learning, or insight.

Of a field of knowledge, intellectual topic, etc.: demanding deep study, research, or consideration; containing great depths of meaning and…

In full accordance with fact, reason, or good sense; founded on true or well-established grounds; free from error, fallacy, or logical defect…

Of study, discussion, etc.: consisting in, or relating to, little-known or abstruse knowledge; esoteric.

Of learning or knowledge.

In general use: Effective, effectual; sound.