From Longman Dictionary of Contemporary Englishcombination lockˌcombiˈnation lock noun [countable] 
TDa lock which can only be opened by using a series of numbers or letters in a particular order
TDa lock which can only be opened by using a series of numbers or letters in a particular orderExamples from the Corpus
combination lock• Next to it was a steel security cupboard fitted with a combination lock.• I took it down from the wall to reveal the circular door of a wall safe with a combination lock.• The case sported matching brass hardware, including a pair of clasps, each with its own three-number combination lock.• The only thing holding me up would be fumbling at the combination lock or renting a towel.• Remember the analogy of the combination lock. 