Once in a while he might gamble a little. Here ‘Once in a while’ meaning -

Once in a while (phrase)Meaning: From time to time; occasionally.Bengali meaning: মাঝে মাঝে; কখনো-কখনো।Correct Sentence: Once in a while he might gamble a little.বাক্যের অর্থঃ কখনো কখনো সে একটু জুয়ো খেলতে পারে।Source: Oxford Dictionary & Bangla Academy Dictionary.