In Herodotus this adverb (from epsilon 2642) occurs at 1.30.3 -- Croesus asks e)pistrefe/ws why Solon considers Tellos (tau 284) so fortunate -- and LSJ's 'earnestly, vehemently' conveys the sense of it there. The Suda's 'deceitfully' repeats one version of the Glosses on Herodotum on the passage. For ps.-Zonaras s.v., which takes over the Suda entry, Tittman's punctuation sought to ameliorate matters ('[Meaning] carefully, in Herodotus. Also [can mean] deceitfully'). How Herodotus 1.30.3 could have been understood as 'deceitfully' remains baffling; note, though, that in a phrase such as ma/la e)pistrefw=s (sic) kai\ r(htorikw=s ...fh/sousin (Aeschines 1.71) the idea of deception might well come in.