This might be just a supplemental entry adding to an entry in the Main Volume.
mæsse-dæg
.Add :-- Eádmund cyning forðférde on Sc̃s Agustínus mæssedæg, Chr. 946; P. 112, 2. On Sćĕ Gregories mæssedæg, 951; P. 112, 7. Se cyng hét ofsleán ealle ðá Deniscan men þe on Angelcynne wǽron on Bricius messedæg, 1002 ; P. 135, 2.
Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "mæsse-dæg." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 628.
, es; m. A festival (v. mæsse, II.) :-- Uton sécan úre cyrcean Sunnandagum and mæssedagum frequentemus ecclesias nostras diebus Dominicis, et diebus festis, L. Ecg. P. iv. 66; Th. ii. 226, 29: Blickl. Homl. 47, 27. Be mæssedaga freólse, L. Alf. pol. 43; Th. i. 92, 1. November onginþ on ealra hálgena mæssedæg, Ælfc. Gr. 9, 18; Som. 9, 56. Uppon sc̃e Laurent mæssedæg. Chr. 1103; Erl. 239, 5. [Orm. messedaȝȝ to freollsenn: Ayenb. messedaȝes holidays.]