Same entry, according to Adler, in the Ambrosian Lexicon (648).
The headword kerwth/ is a mis-spelling of kairwth/ (Trapp s.v.), glossed as "Gewebe", "fabric". Trapp cites it as attested here and in the orthographic lexica edited by Ludwich (1905-1912) 198.12, both with that spelling. Compare generally kappa 1193, kappa 1195, and the adjective kairwto/s "well-woven?" in Callimachus fr.383 Pfeiffer (noted in the Supplement to LSJ); all derived from kairo/w "fasten threads on the loom", which in turns comes from kai=ros "row of thrums in the loom, to which the threads of the warp are attached, ravel" (LSJ s.v.).
The gloss is equally rare. In Ludwich's lexicon it is spelled milwth/ (Trapp s.v.), but perhaps incorrectly: the related mi/twma "cords on the loom for attaching a warp; threads" and mitwth/s "inspector of silk threads" are attested in other Byzantine texts (Trapp s.vv.), and cf. in any event mu 1135.
Although the nouns are both substantially unattested, they both involve weaving of fabric. Eustathius defines kai=ros explicitly as mi/twma (Commentary on the Iliad I p. 241, III p. 399; this corroborates kairwth/ and mitwth/ being synonyms.