Intact and Undiminished

Intact adjective - Not lacking any part or member that properly belongs to it.

Undiminished and intact are semantically related in whole topic. In some cases you can use "Undiminished" instead an adjective "Intact", when it comes to topics like amount.

Undiminished adjective - Not lessened or diminished.

Intact and undiminished are semantically related in amount topic. You can use "Intact" instead an adjective "Undiminished", if it concerns topics such as complete, total.