Green’s Dictionary of Slang

1. to greet someone by raising the arm and ritualistically slapping each other’s palm.

1997		G. Sikes 8 Ball Chicks (1998) 34: She laughed and she and Romero high-fived each other.
1999		K. Sampson Powder 190: Everybody high-fived him.
2006		C.W. Ford Deuce’s Wild 5: JJ ‘hi-fived’ me as he sauntered in.

2. to slap hands as a form of celebration, affirmation, congratulation etc.

1990		S. Morgan Homeboy 18: The troop laughed and highfived, declaring victory by default.
2005		P. Howard Curious Incident of the Dog in the Nightdress 242: He high-fives me, he actually high-fives me.
2012		L. Jose ‘Underhooks’ in Crime Factory: Hard Labour [ebook] Some of the younger men high-fived each other and screamed.
2012		R. Milward Kimberly’s Capital Punishment (2023) 490: Some of my weekly exes high-five each other.
2017		S.M. Jones August Snow [ebook] I didn’t high-five him. Instead I gave him a spare key to the house.
2020		C. Hiaasen Squeeze Me 126: Uric [...] high-fived himself. Jauntily he bounded out of the van.
2021		L. McInerney Rules of Revelation 93: [S]he saw that they were not cackling or high-fiving.