The term 'speak unclearly' can be described by three different crossword solutions: MUTTER (6 letters), SLUR (4 letters), and MUMBLE (6 letters). MUTTER is a low, indistinct sound made with closed lips, usually expressing dissatisfaction or other strong emotion. SLUR is to speak indistinctly or unintelligibly, often as a result of intoxication or illness. MUMBLE is to speak in a low indistinct voice, often barely audible. All three words describe speaking in an unclear manner, either due to emotion, intoxication, illness, or simply speaking too quietly.