This might be just a supplemental entry adding to an entry in the Main Volume.
dóm-bóc
.Add :-- Ic gedó þ̵ man sceall þé wel fæste gewríðan, and þé, eall swá seó dómbóc be swilcum mannum tǽcð, oft and gelóme swingan, Hml. S. 23, 714. [v. N. E. D. doom-book.]
Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "dóm-bóc." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 154.
;f. [bóc a book, q. v.] DOOM-BOOK, a book of decrees or laws; lĭber judĭciālis :-- Béte be ðam ðe seó dóm-bóc secge let him pay a fine according as the doom-book may say, L. Ath. i. 5; Th. i. 202, 7: L. Edg. i. 3; Th. i. 262, 23: i. 5; Th. i. 264, 20. Swá hit on ðære dóm-béc stande as it stands in the doom-book, L. Ed. prm; Th. i. 158, 4. Ne þearf he nánra dómbóca óðerra cépan he need not heed any other doom books, L. Alf. 49; Th. i. 56, 30.