Loosen vs Undefined - What's the difference?

As a verb loosen

is to make loose.

lacking a definition or value.

(en verb)

To make loose.

to loosen a knot

After the Thanksgiving meal, Bill loosened his belt.

* Francis Bacon

After a year's rooting, then shaking doth the tree good by loosening of the earth.

To free from restraint; to set at liberty.

* Dryden

It loosens his hands, and assists his understanding.

To remove costiveness from; to facilitate or increase the alvine discharges of.

(Francis Bacon)

* tighten

* loosen the apron strings * loosen the purse strings * loosener

(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