indefinable

Impossible to define, describe, or analyze.

Not definable; incapable of being defined or exactly described; not susceptible of definition: as, an indefinable boundary; an indefinable word; indefinable sensations.

Incapable of being defined or described; inexplicable.

That cannot be precisely defined or put into words

That defies description; indescribable

Anything that cannot be defined.

not capable of being precisely or readily described; not easily put into words

defying expression or description