The term 'close in on' can be broken down into four crossword solutions: THREATEN (8 letters), GAIN (4 letters), NEAR (4 letters), and ZERO (4 letters). To 'close in on' something is to approach it, usually with the intention of achieving a goal. To THREATEN something is to make it aware of potential danger or harm, while to GAIN something is to acquire it. NEAR implies proximity, and ZERO suggests that the goal is close to being achieved. Together, these words suggest that one is approaching a goal with the intention of acquiring it, and is close to achieving it.