Undefinable Synonyms

An undefinable something about the room seemed to suggest masculine habitation.

For example, have you tried to set down some of your own reveries or more undefinable feelings?

And as the undefinable essence of the force moving the heavenly bodies, the undefinable essence of the forces of heat and electricity, or of chemical affinity, or of the vital force, forms the content of astronomy, physics, chemistry, botany, zoology, and so on, just in the same way does the force of free will form the content of history.