A word clearly derived from the root √ENED “middle”. In the context of Elvish psychology, Tolkien described it as:

This we translate “heart”, though it has no physical reference to any organ of the hröa [body]. It means “centre”, and refers (though by inevitable physical allegory) to the fëa [spirit] or sáma [mind] itself, distinct from the periphery (as it were) of its contact with the hröa (VT39/32).

Neo-Quenya: For purposes of Neo-Quenya, I would assume this word can also be used physically to refer to the “interior” of something.