Part of Speech-Adjective

Definition-Too great, powerful, beautiful/ to be described or expressed

Source–http://www.merriam-webster.com/dictionary/ineffable

Encountering of Word-“The hearing of those wild notes always depressed my spirit, and filled me with ineffable sadness.”

Understanding-I know understand that the author was saying that the sadness was too great to be describe or expressed. It was basically unexplainable.