[By a slip, the SOL headword is the secondary one in the entry, braxe/sin.]
[1] The headword -- evidently quoted from somewhere -- is unattested outside lexicography, the gloss (also in Photius and elsewhere) commonplace. Both are in an oblique case here, either accusative plural or more probably genitive singular.
[2] 'short' here is braxe/sin, dative plural of the adjective that contributes the first element of the headword. Again, it is evidently extracted from somewhere.