means To shine with a soft, wavering, broken light — the way water, silk, or heat off pavement seems to quiver as it catches the eye.

from From Old English 'scimerian,' to glitter or glisten, built on the same Germanic root as 'shine' (Old English 'scinan'). The '-er' ending is the language's way of making a word flicker — a frequentative, marking a thing done repeatedly, in little bursts. So where 'shine' is one steady beam, 'shimmer' is shine stuttering, light caught trembling over and over. It has close cousins in German 'schimmern' and Dutch 'schemeren,' all glimmering off that same old root for brightness.