one-track mind
A mindset or line of thinking that is fixated upon or preoccupied by a particular topic. Jerry, you have such a one-track mind—not everything has to do with sex. My sister has a one-track mind, only thinking about how something can further her career.
one-track mind
Fig. a mind that thinks 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.
one-track mind
A mind limited to only one line of thought or action, as in All you think about is sex-you have a one-track mind. This expression, alluding to a train that runs only on one track or in one direction, was first recorded in 1928.
one-track mind
n. a (person’s) mind obsessed with only one thing. When it comes to food, Tom has a one-track mind.