Hróst-beág

According to the Old English Dictionary:

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hróst-beág

the woodwork of a circular roof :-- Tigelum sceádeþ hróstbeáges hróf [MS. hrost beages rof] the woodwork of the roof parts from the tiles, the tiles fall off leaving the woodwork of the roof bare, Exon. 124 a; Th. 477, 29; Ruin. 32. hrost-beag