Mano-dhātu: 'mind-element', is one of the 18 elements see: dhātu II. This term, unlike manāyatana does not apply to the whole of consciousness, but designates only that special element of consciousness which first, at the beginning of the process of sense-perception, performs the function of directing āvajjana a href=dic2-abbrev.htm#Tab. Tab. I, 70 to the sense-object and, then after twice having become conscious of it performs the function of reception sampaticchana into mind-consciousness.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.