rap at

rap at (someone or something)

1. To strike something with one or more quick, light blows, as when getting someone's attention; to knock or tap at something swiftly and lightly. I thought I heard someone rapping at my window in the middle of the night, so I was wide awake with fear until morning! The wind was causing a tree branch to rap at the door in a most unsettling manner.
2. To utter spoken word rhymes meant to mock or denigrate another person during a rap battle. You've got to have thick skin when someone's rapping at you, but you also have to know that it's all just part of the game.
See also: rap
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

rap at something

 and rap on something
to tap on something to attract someone's attention. Who is that rapping at my door? Someone is rapping at the window, trying to get my attention. I will rap on her window and try to wake her.
See also: rap
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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References in classic literature ?
"That is another point (replied he;) We must not pretend to determine on what motive the person may knock--tho' that someone DOES rap at the door, I am partly convinced."
The tea things were brought in, and already had Marianne been disappointed more than once by a rap at a neighbouring door, when a loud one was suddenly heard which could not be mistaken for one at any other house, Elinor felt secure of its announcing Willoughby's approach, and Marianne, starting up, moved towards the door.
class=Country artist Kacey Musgraves won album of the year for "Golden Hour", while "This is America" by Childish Gambino won both record and song of the year at the 61st Grammy Awards on Sunday in a breakthrough for rap at the most prestigious honors in the music business.British pop singer Dua Lipa was named best new artist and popular rapper Cardi B won her first Grammy, taking best rap album for "Invasion of Privacy.
UCSF's Academic Senate and the Helen Diller Family Comprehensive Cancer Center joined RAP at a later date.
Researchers evaluated plant-produced mixtures with high RAP content (25 and 40 percent), different binders (PG64-22 and the softer PG58-28), and a control mixture with no RAP The study improved the understanding of the performance characteristics of hot-mix asphalt (HMA) mixtures with RAP at high, intermediate, and low temperatures and examined plant-produced HMA mixtures containing RAP.
The 28-year-old Science Communication student at the University of Glamorgan has also been asked to perform his rap at the Science Museum in London on Wednesday evening.
Rap at best, she says, is a "petition," a plea from young people to look at their lives.