'gambling-friendly' originates from English, specifically the compound of 'gambling' (the present participle of 'gamble') and 'friendly' (from Old English 'freond' with the adjectival suffix '-ly'), where 'gamble' originally referred to playing or wagering and 'friendly' meant 'having the quality of a friend / being favorable to'.

'gamble' developed in Middle English from verbs related to play and pastime (e.g. Middle English 'gamblen'/'gamen' and possibly influenced by 'gambol'), eventually becoming the modern verb 'gamble'; 'friendly' comes from Old English 'freondlic' (related to 'freond' = 'friend') which became Middle English 'friendlich' and later modern English 'friendly'; the compound 'gambling-friendly' is a recent productive formation combining the gerund/present-participle form with 'friendly'.

Initially, the parts referred separately to 'wagering/play' ('gambling') and 'having the qualities of a friend or being favorable' ('friendly'); over time, their compound use came to mean 'favourable to or accommodating of gambling' specifically.