Wiktionary
alt. A hammer having, besides the normal flat head, an opposite, rounded or peen head. n. A hammer having, besides the normal flat head, an opposite, rounded or peen head.
WordNet
n. a hammer with one round and one flat end; used in working metal
Wikipedia
A ball-peen (also spelled ball-pein) hammer, also known as a machinist's hammer, is a type of peening hammer used in metalworking. It is distinguished from a cross-peen hammer, diagonal-peen hammer, point-peen hammer, or chisel-peen hammer by having a hemispherical head. It is commonly used as a tool for metalworking.
Usage examples of "ball-peen hammer".
It went overhead this time, and the ball struck rock barely submerged a few hundred meters to their left, with a sound like an enormous ball-peen hammer on granite.
Amazing, the persuasive powers of a two-pound ball-peen hammer applied to a kneecap.
The issue was Angel, lone baby in an otherwise childless building: her crying (though she rarely cried), her noisy play (though Angel wasn't yet strong enough to shake a rattle), and the potential she represented for damage to the premises (though she was not yet able to get out of a bassinet on her own, let alone go at the plaster with a ball-peen hammer).