Robert Ellis (3 February 1812 – 19 August 1875; sometimes spelt Elis), professionally known by his bardic name Cynddelw (after a 12th-century poet of the same name), was a Welsh language poet, editor, and lexicographer, born at Tyn y Meini, Bryndreiniog, Pen-y-Bont-Fawr in the old county of Montgomeryshire, Mid Wales.
He was also a Baptist minister: from 1836 to 1840 at Llanelian-yn-Rhos and Llanddulas, Denbighshire; from 1838-1840 Glyn Ceiriog in the Ceiriog Valley; from 1847 to 1862 at Tredegar, Monmouthshire; and from 1862 until his death in 1875, at Caernarfon.
His poem Yr Adgyfodiad was published in 1849, whilst he was a minister at Tredegar in the Sirhowy Valley. Many other poems, biographies, an autobiography, and a dictionary followed. His dictionary, Geiriadur Cymreig Cymraeg, published in Caernarfon in 1868 was one of the first dictionaries to be published only in Welsh (rather than English and Welsh).