Blithe vs Undefined - What's the difference?

As adjectives the difference between blithe and undefined

is that blithe is (dated or literary) happy, cheerful while undefined is lacking a definition or value.

(er)

(dated or literary) Happy, cheerful.

Indifferent, careless, showing a lack of concern.

She had a blithe disregard of cultures outside the United States.

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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