The term 'PART OF A PUMP' can be broken down into four crossword solutions: INSOLE (6 letters), SOLE (4 letters), HEEL (4 letters), and INSTEP (6 letters). The insole is the inner SOLE of a shoe, which is usually made of cushioning material to provide comfort and support. The SOLE is the bottom of the shoe, which is typically made of rubber or leather and provides traction. The HEEL is the back of the shoe, which is usually thicker than the rest of the SOLE and provides stability. The instep is the top of the shoe, which is usually curved and provides support for the foot.