The headword phrase, otherwise unattested, is presumably quoted from somewhere, and seems (in DW's view at least) to cry out for a negative, as supplied above. Be that as it may:
(i) Its adverb sxedi/ws (temporarily, sketchily, at random) is cognate with the adjective sxe/dios (close, casual, temporary, off-hand); cf. sigma 1770, sigma 1771, sigma 1773, sigma 1774, sigma 1775, sigma 1776, sigma 1778, and see generally LSJ s.v.
(ii) Its verb form, attested only here, is the second person singular, aorist imperative passive, of the verb e)ktre/pw, I turn astray, go off course; see generally LSJ s.v.
The thought conveyed by the phrase (if a negative is supplied: see above) finds a parallel of sorts in Aratus, Phaenomena 1.1153-54. Featuring the earliest attestation of the headword adverb, it advises ancient astronomers tw=n a)/mudis pa/ntwn e)skemme/nos ei)s e)niauto\n ou)de/pote sxedi/ws ken e)p’ ai)qe/ri tekmh/raio, By having observed all things together throughout the year, you would never judge at random from the sky.