"afraid to say what one really thinks," 1570s; first element perhaps from Old English milisc "sweet," from Proto-Germanic *meduz "honey" (see mead, n.1), which suits the sense, but if the Old English word did not survive long enough to be the source of this, perhaps the first element is from meal, n.2 on notion of the "softness" of ground flour (compare Middle English melishe (adj.) "friable, loose," used of soils).