fæstnes
This might be just a supplemental entry adding to an entry in the Main Volume.
Related §§ in Wright's OE Grammar:
In the OE text, the length is:indicated by acute accentsindicated by macronsnot indicated.
fæstnes
Add:1. stability. v. fæst; III. Þæs wealles micelness and fæstness murorum firmitas et magnitudo , Ors. 2, 4; S. 74, 14. 2. tenacity. Cf. fæst; I. [ Seó fastnysse þæs yfeles wǽtan on þan heáfede, Lch. iii. 130, 7.] 3. resolution, vigour, firmness. Cf. fæst; II. Sameramis féng tó þám ríce mid mycelre fæstnesse (réþnesse, v. l. ) and wrǽnnesse (cf. Ors. 1, 2; S. 30, 14-35), Ors. 1, 2 tit. ; Th. 513, 4. v. ymb-fæstness.
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A Combined List of Abbreviations.

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A Combined List of Abbreviations.