suspicious adj.

early 14c., "suspected of wrongdoing, under or open to suspicion;" mid-14c., "regarded with mistrust, liable to arouse suspicion," from Old French suspect (14c.), from Latin suspectus "suspected, regarded with suspicion or mistrust," past participle of suspicere "look up at, look upward," figuratively "look up to, admire, respect;" also "look at secretly, look askance at," hence, figuratively, "mistrust, regard with suspicion." This is from assimilated form of sub "up to" (see sub-) + specere "to look at" (from PIE root *spek- "to observe"). The notion behind the word is "look at secretly," hence, "look at distrustfully." Related: Suspectly.

Proto-Indo-European root meaning "to observe."

It forms all or part of: aspect; auspex; auspices; auspicious; bishop; circumspect; conspicuous; despicable; despise; episcopal; especial; espionage; espy; expect; frontispiece; gyroscope; haruspex; horoscope; inspect; inspection; inspector; introspect; introspection; perspective; perspicacious; perspicacity; prospect; prospective; respect; respite; retrospect; scope; -scope; scopophilia; -scopy; skeptic; species; specimen; specious; spectacle; spectacular; spectrum; speculate; speculation; speculum; spice; spy; suspect; suspicion; suspicious; telescope.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit spasati "sees;" Avestan spasyeiti "spies;" Greek skopein "behold, look, consider," skeptesthai "to look at," skopos "watcher, one who watches;" Latin specere "to look at;" Old High German spehhon "to spy," German spähen "to spy."