The headword is present middle/passive participle, feminine nominative singular, of bri/qw. It might be generated by the quotation given, where it is in the corresponding genitive, but more probably it is extracted from somewhere in its own right; and the likeliest possibility is Homer, Iliad 8.307 (where it occurs in a simile comparing the head of the dying Gorgythion to that of a poppy); cf. the scholia there.
See also beta 540, beta 541, beta 542.
[1] Same or similar glossing in other lexica.
[2] Greek Anthology 6.27.8 (Theaetetus Scholasticus), a retiring fisherman's dedication. See additional quotes from this epigram at alpha 2733 and epsilon 3990.