Real Dictionary

rut
If you say that someone is in a rut, you disapprove of the fact that they have become fixed in their way of thinking and doing things, and find it difficult to change. You can also say that someone's life or career is in a rut.
The rut is the period of the year when some animals such as deer are sexually active, and the males fight each other to mate with the females.
countable noun: A rut is a deep, narrow mark made in the ground by the wheels of a vehicle.

rut in American English 1
a groove, furrow, or track, esp. one made in the ground by the passage of wheeled vehicles
to make a rut or ruts in
noun: a furrow or track in the ground, esp. one made by the passage of a vehicle or vehicles
transitive verb: to make a rut or ruts in; furrow

rut in American English 2
the periodic sexual excitement, or heat, of certain mammals: applied esp. to males, often specif. to those male ruminants in which it occurs once a year
to be in rut
intransitive verb: to be in the condition of rut
noun: the periodically recurring sexual excitement of the deer, goat, sheep, etc

rut in British English 1
noun: a groove or furrow in a soft road, caused by wheels
verb: to make a rut or ruts in

rut in British English 2
noun: a recurrent period of sexual excitement and reproductive activity in certain male ruminants, such as the deer, that corresponds to the period of oestrus in females