un- Definition

un-
prefix

1. Denoting the opposite of the base word; not.
2a. Denoting reversal of an action, process or state;

Example: uncurl
Example: unharness
2b. Denoting an intensification of the base word.

Example: unloosen
3. chiefly archaic
Denoting release or removal from or deprivation of.
Example: ungarter
Example: unfrock

Etymology: Anglo-Saxon.

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unadvisable

1. Said of a person: not open to advice; obstinate.
2. Said of a course of action, etc: inadvisable.

Derivative: un-
noun

Advisableness

Derivative: unadvisably
adverb

Etymology: 17c.