The term BALL PEEN HAMMER is a type of HAMMER that has two heads, one flat and one rounded. The flat head is called the peen and is used for shaping metal, while the rounded head is used for striking. The crossword solutions for this term are PEEN (4 letters) and TEEN (4 letters). PEEN is an alternate spelling of the word 'pein', which is the flat head of the HAMMER, and TEEN is a shortened form of the word 'teenage', which is often used to describe the rounded head of the HAMMER.