Martial vs Undefined - What's the difference?

As a proper noun martial

is narrowly applied to certain historic persons (but some of its foreign cognates are modern given names).

lacking a definition or value.

(en adjective)

Of, relating to, or suggestive of war; warlike.

* Dryden

But peaceful kings, o'er martial people set, / Each other's poise and counterbalance are.

Relating to or connected with the armed forces or the profession of arms or military life.

(comparable) Characteristic of or befitting a warrior; having a military bearing; soldierly, soldierlike, warriorlike.

(medicine, chemistry, obsolete) Relating to, or containing, iron; chalybeate.

martial preparations

martial flowers: a reddish crystalline salt of iron

* court martial * martial art * martialism * martialness * martialist * martial law * martially

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(wikipedia undefined) (-)

Lacking a definition or value.

(mathematics, computing) That does not have a meaning and is thus not assigned an interpretation.

The result of division by zero is undefined .

* defined