Mewl is a term used to describe the sound made by a baby when they are crying or whining. It is a soft, high-pitched sound that is often associated with infants and young children. The term 'whine like a baby' is often used to describe someone who is complaining or expressing dissatisfaction in a high-pitched, whiny voice. The crossword solution for this phrase is MEWL, which is a four-letter word that accurately describes the sound of a baby whining.