From Longman Dictionary of Contemporary Englishodds-onˌodds-ˈon adjective 1 → odds-on favourite2 British English informalHAPPEN very likelyit’s odds on (that) It’s odds on that she won’t come.be odds-on to do something They must have felt they were odds-on to win.
Examples from the Corpus
odds-on• The media regarded Gorbachev as the odds-on favorite to dethrone the old champ.• Personally, I was excited at the prospect of participating in a real blood-and-guts battle against a prohibitive odds-on favorite.• Laing built the original centre 10 years ago and is odds-on to carry out the work if the scheme gets the nod.• But Schuey was in top form and the triple world beater always looked odds-on to score his fifth win on the trot.be odds-on to do something• Laing built the original centre 10 years ago and is odds-on to carry out the work if the scheme gets the nod.• Unsurprisingly, Rugby missed their putt, falling behind when they must have felt they were odds-on to go ahead. 