Same or similar entry in other lexica; references at Photius alpha1077 Theodoridis. The headword is accusative plural of the noun a)lfo/s, defined by LSJ as "dull-white leprosy, esp. on the face". (It is cognate with Latin albus; cf. the compounds a)lfopro/swpos "white-faced" and a)lfo/rugxos "white-snouted".)
This accusative plural must be quoted from somewhere -- probably Plato, Timaeus 85A, leu/kas a)lfou/s. The glossing aims to point out that, since a)lfo/s is masculine, one could just as well write leukou/s.