þurh-seón
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.
þurh-seón
AddHé þurhseah swá þone preóst for ðon gesealdne deófle, gif hé gedyrstlǽhte hé underféngce ðone hálgan sácerdhád perspexit hunc clericum idcirco diabolo traditum, ne ad sacrum ordinem auderet accedere, Gr. D. 136, 6.
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.