Learner's definition of PERIL
somewhat formal + literary
1 [noncount] : the possibility that you will be hurt or killed or that something unpleasant or bad will happen : danger — usually used in the phrase in peril 2 [count] : something that is likely to cause injury, pain, harm, or loss : danger — usually plural
at your (own) peril
— used to say that if you do something you should be aware that it is dangerous and that you could be harmed, injured, punished, etc.