Synonyms for Conniving (same or very similar meaning)
WordNet sense 1 (acting together in secret toward a fraudulent or illegal end):
collusive
WordNet sense 2 (secret or hidden; not openly practiced or engaged in or shown or avowed):
covert
WordNet sense 3 (used of persons):
calculating, calculative, scheming, shrewd
WordNet sense 4 (dispassionate):
hard
From the ODE community, based on WordNet
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