定音鼓（意大利语：Timpani，西班牙语：Tímpano，英语：Timpani或Kettledrum，德语：Pauken，法语：Timbales，）是一种膜鸣乐器，由古代战争时的战鼓所演变出来的变种乐器。在巴洛克时代后期开始在乐队中使用，古典时期起已成为了常规化的乐器，亦成为了整个交响乐团中的一个重要乐器。

现时定音鼓较常采用的外语名称为意大利语的timpani，是源自于意大利语，为timpano的复数形。这个字的起源来自希腊字τύμπανον（tumpanon，复数为tumpana），经过拉丁字母化后，变成tympanum（复数：tympani），意思为「敲打」。 不过自定音鼓出现于乐队起，绝少情况下只使用一只，因此通常都会使用复数形。另外，18世纪、19世纪的英、美地区亦会写作timpany、tympani或tympany等。现代英、美作曲家则较常用Kettledrum一字。

Timpani (/ˈtɪmpəni/; Italian pronunciation: [ˈtimpani]), or kettledrums (also informally called timps), are musical instruments in the percussion family. A type of drum, they consist of a skin called a head stretched over a large bowl traditionally made of copper. They are played by striking the head with a specialized drum stick called a timpani stick or timpani mallet. Timpani evolved from military drums to become a staple of the classical orchestra by the last third of the 18th century. Today, they are used in many types of musical ensembles, including concert bands, marching bands, orchestras, and even in some rock.