Dwimmerlaik -- Anglo Saxon dwimor 'phantom'; the last element is stated to derive from Old Norse -leikr, Old English -lac '-like'. Eowyn's term somewhat understates the description of the Lord of the Nazgûl, the Witch King of Angmar.
Of passing interest, concerning your pic of Eowyn; the Lord of the Nazgûl attacked her with a huge mace in the film. Peter Jackson kept turning down the mace provided by the film's production designer saying that it was too small; each successive prop provided was rejected by Jackson as too small. The giant war hammer seen in the film apparently satisfied Jackson's intent.
