'innocent-looking' is a compound of 'innocent' and 'looking'. 'innocent' originates from Latin, specifically the word 'innocentem' (from 'in-' meaning 'not' + 'nocere' meaning 'to harm'), and 'looking' comes from the verb 'look', which originates from Old English 'lōcian'.

'innocent' entered English via Old French and Middle English from Latin 'innocentem', eventually becoming the Modern English 'innocent'. 'look' evolved from Old English 'lōcian' to Middle English forms such as 'loken'/'loken' and then modern 'look'; the compound form 'innocent-looking' is a productive modern English adjective formed by joining an adjective and a present-participial form.

Initially, 'innocent' carried senses of 'not causing harm' or 'not guilty'; over time it also acquired senses of 'naive' or 'unsophisticated'. Combined with 'looking', the compound came to mean 'appearing to be innocent' (emphasis on appearance rather than actual innocence).