'suspicious-looking' originates from Modern English by combining the adjective 'suspicious' and the present participle 'looking' (from 'look'). 'suspicious' ultimately comes via Middle English and Old French from Latin 'suspicari', where 'sus-'/ 'sub-' and 'specere' related to looking or observing.

'suspicious' changed from Latin 'suspicari' into Old French forms (e.g. 'suspicieux') and Middle English 'suspicious', eventually becoming the modern English 'suspicious'. 'look' changed from Old English 'lōcian' (to look) into the modern English verb 'look', and the compound 'suspicious-looking' arose by combining the adjective with the present participle.

Initially, elements related to 'suspicious' meant 'to suspect or look upon' (i.e., to observe with doubt); over time the combined expression came to mean 'appearing to deserve suspicion' or 'giving an impression of being untrustworthy'.