Dictionary.com
Thesaurus.com

best part of something

Idioms  

  1. Nearly all of something, the majority, as in The dentist was late; I waited for the best part of an hour. The adjective best here does not concern quality but quantity. [First half of 1500s] Also see better half, def. 1.

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.