ymb-gangan
This might be just a supplemental entry adding to an entry in the Main Volume.
In the OE text, the length is:indicated by acute accentsindicated by macronsnot indicated.
ymb-gangan
Add: to surround, encompass 'Send mé þínne engel on fýrenum wolcne þæt þá embgange ealle þás ceastre þæt ne magen geneósian for þsém fýre.' And þus cweþende fýren wolc[n] ástáh of heofonum, and hit ymbsealde ealle þá ceastre, Bl. H. 245, 29.
This is a supplementary entry with editorial changes to an entry in the main volume of the dictionary. Look under the 'Possibly connected entries' below, or for the same headword in the list to the left.

A Combined List of Abbreviations.

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A Combined List of Abbreviations.