'hollowly' originates from English, formed from the adjective 'hollow' + the adverbial suffix '-ly' (ultimately from Old English suffix '-lice').

'hollow' changed from Old English 'holh' (or 'hol') to Middle English forms such as 'holwe'/'holowe' and eventually became modern English 'hollow'; the adverbial ending developed from Old English '-lice' into Middle English '-ly', producing 'hollowly'.

Initially, it meant 'having a cavity' or 'full of a hole'; over time it also acquired figurative senses of 'lacking substance' or 'insincere', which 'hollowly' expresses adverbially.