Transferred use of the Scottish surname. The principal family bearing this surname were hereditary Earls Marischal of Scotland from 1455 to 1715. This is one of a number of Scottish aristocratic surnames that have become well established since the 19th century as boys' names throughout the English-speaking world, not just in Scotland. Others include Bruce, Douglas, and Graham.
English: from Middle English more ‘moor’, ‘marsh’, ‘fen’, ‘area of uncultivated land’ (Old English mōr), hence a topographic name for someone who lived in such a place or a habitational name from any of the various places named with this word, as for example Moore in Cheshire or More in Shropshire.