Linguistically, he word ‘Khimar’ or ‘Khumur’ (it's plural) comes from the root 'خ م ر' which means something which veils or conceals.
Nowadays Khimar typically refers to a very long piece of cloth, tailored in a specific manner, with or without headbands, that falls from the head to cover the neck, chest, elbows and hands. Depending wearer's preference, it may extend to the knees or even the feet. Unlike a Hijab or a Headscarf, a Khimar usually doesn't require tying around the neck, which is convenient and comfortable for the user.
