The headword, attested only here (and, according to Adler, in the Ambrosian Lexicon [424]), is evidently an adjective -- not in LSJ -- in the neuter nominative/accusative singular.
[In her critical apparatus Adler reports that the supplementary part of the entry is lacking in mss AF.]
[1] For kolobo/s (docked, curtailed, shortened, maimed) with simo/s see kappa 1941; cf. sigma 437, lambda 860 (gloss), omega 275 (gloss), and sigma 436.
[2] Adler reports that ms V splits and rewrites the passage, placing simo\s o( e)k tou= k. to\ k. a)po\ tou= noo/s after sigma 429 and inserting h)/toi tou= sw/|ou to\ h(/misu h)\ e)k tou= sismo/s, o(\ shmai/nei to\n kolobo/n, gi/netai simh/sion after sigma 431; also that ms A inserted into the margin *simh/sion to\ p. h(mi=n sw/|ou to\ h(/misu, kai\ simh/sion e)k tou= simo/s, o(\ shmai/nei to\n kolobo/n.