Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† hălōs, ō, f., = ἅλως (a round threshing-floor), a circle round the sun or moon, a halo, pure Lat. corona: circa solem visum coloris varii circulum, qualis esse in arcu solet. Hunc Graeci halo vocant: nos dicere coronam aptissime possumus, etc., Sen. Q. N. 1, 2, 1.
Called also hălysis (prob. corrupted from ἅλως), App. de Mundo, p. 64, 16.