A dull speaker is someone who speaks in a monotonous and uninteresting way. The crossword solutions for this term are 'DRONE' (5 letters) and 'BORE' (4 letters). DRONE refers to the sound of a low humming noise, which can be used to describe the sound of a dull speaker's voice. BORE, on the other hand, is a word used to describe something that is tedious and uninteresting, which is an apt description of a dull speaker's speech.