brown-nose (v.)

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, quoted in OED]. Related: Brown-noser, brown-nosing (both 1950). British bumsucker "sycophant" is attested from 1877.