The term 'SIT STILL FOR' can be broken down into two crossword solutions: LET (3 letters) and POSE (4 letters). The phrase 'sit still for' is an idiom that means to remain in a certain position or situation without moving or changing. It is often used when someone is asked to remain in a certain position for a photograph or other type of image. In this context, the word 'LET' implies permission to remain in the position, while 'POSE' implies the act of remaining in the position.