also brownnose, 1939, American English colloquial, said to be military slang originally, from brown (adj.) + nose (n.), "from the implication that servility is tantamount to having one's nose in the anus of the person from whom advancement is sought" [Webster, 1961]. Related: Brown-noser, brown-nosing (both 1950).
also brown-noser: He got there by being a pious and effective brown-nose
To flatter and pamper in order to gain approval and advantage; curry favor; apple-polish: He's just like any other person who's in a position to screw you. You gotta brown nose
[1930s+ Military academy students; fr the color of feces presumably acquired when one has one's nose at the flatteree's anus]