Fig. to think entirely or almost entirely about one subject. Adolescent boys often have one-track minds. All they're interested in is the opposite sex.Bob has a one-track mind. He can only talk about football.
if someone has a one-track mind, they seem to talk and think about one particular subject all the time, especially sex 'I bet I know what you two were doing last night.' 'Oh, shut up, Sean, you've got a one-track mind.'You've got to have a one-track mind if you want to succeed in business.