dossard
A bib attached to the back of a cyclist's shirt that carries the cyclist's race number.
[Bernard] Hinault will also be wearing a 51 dossard, the same number with which Luis Ocana, [Bernard] Thevenet, [Eddy] Merckx, and [Jacques] Anquetil pedalled to victory in their first Tour.
Where it comes from
Borrowed from French dossard, from dos (“back (of a person)”) (ultimately from Latin dorsum (“back of the body”), further etymology uncertain) + -ard (suffix forming nouns indicating things belonging to or representing particular classes or sorts).
Adapted from the Wiktionary entry dossard (CC BY-SA 4.0).