met ‧ ro ‧ nome /ˈmetrənəʊm $ -noʊm/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: Greek ; Origin: metron ( ⇨ ↑ -meter ) + -nomos 'controlling' (from nomos 'law' ) ]
a piece of equipment that makes a regular repeated sound like a clock, showing the speed at which music should be played