The crossword solution for the term ONE MAY BE DULL is ACHE, which is a four-letter word. ACHE is a verb that means to have a continuous dull pain or a feeling of mental or emotional distress. It can also be used to describe a longing or yearning for something. ACHE is often used to describe physical pain, such as a headache or muscle ACHE, but it can also be used to describe an emotional pain, such as heartache or homesickness.