I need a word to describe a word [duplicate]

weasel word

noun

a word used in order to avoid being clear or direct.
— Merriam-Webster's Learner's Dictionary.

noun

a word used in order to evade or retreat from a direct or forthright statement or position "Reorganization” is just a weasel word that the company is using to say that jobs are being eliminated.
— M-W

How about ambiguous or vague?

M-W:

ambiguous: able to be understood in more than one way : having more than one possible meaning; not expressed or understood clearly

vague: not clear in meaning; stated in a way that is general and not specific

Your example:

The importance of a factor depends on how importance is defined. The word importance has a fuzzy nature open to different interpretations and the importance of a factor depends on how importance is defined.

In other words, importance is ambiguous or vague.

Other possibilities are (too) general and non-specific.