best part of something
the best part of (something)
1. The majority of something. I'm sorry I'm late—my doctor's appointment took the best part of an hour.
2. The most enjoyable or exemplary aspect of something. No, the cream filling is definitely the best part of this dessert! The introduction was the best part of your term paper. After that, it meandered for a while.
best part of something
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.