From Longman Dictionary of Contemporary Englishnumber oneˌnumber ˈone1 noun 1 BESTFAVOURITE/FAVORITE[uncountable] the best, most important, or most successful person or thing in a group Until his marriage, his job was number one in his life. Shearson is number one in the market this year.2 APMAMT[countable, uncountable] the musical record that is the most popular at a particular time number one in the charts They’ve had three number ones.3 → look out for number one4 [singular, uncountable] spoken informal a word meaning urine, used especially with children to avoid saying this
Examples from the Corpus
number one• Diana's children were always number one in her life.• The song was number one in the charts for two months.number oneˌnumber ˈone2 adjective 1 IMPORTANTmost important or successful in a particular situation The University of Maine has the number one hockey team in the country. Sweden’s number one model2 FIRSTfirst on a list of several things to be considered, done etc item number one on the agenda This has got to be our number one task.Examples from the Corpus
number one• Number one - always lock doors and windows.• Safety is our number one concern.• California is the number one travel destination in the U.S. 