Definition of "bract"

In this vegetable monster the bractes, or divisions of the spike, become wonderfully enlarged; and are converted into leaves.

1789, Erasmus Darwin, The Loves of the Plants, J. Johnson, page 9

A Verticil or Whirl may be […] Naked; that is without involucre, bracte or brittle. Bracted - or Involucred

1793, Thomas Martyn, The Language of Botany

Great dense patches of them grew, four and five and six feet deep, impenetrable swathes of dark green bracts that advertised their danger.

2017, Benjamin Myers, The Gallows Pole, Bloomsbury, published 2019, page 31