The term 'CAUSING A PUCKER' can be solved by the four-letter word 'TART'. This word is used to describe something that is sharp or acidic in taste, often referring to a food or drink. It can also be used to describe someone or something that is unpleasantly sharp or severe in manner or style. In this context, it implies that the thing being described is causing a pucker, or a wrinkling of the skin due to a sour or bitter taste.