the big something-o

the big (number)-o

An age ending in zero, used especially when one turns that age on one's birthday. So, you're turning the big three-o tomorrow! How are you feeling about it? My mom's going to be the big six-o this summer, so we're planning a big family vacation to mark the occasion.
See also: big
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

the big — -o

used to denote an age ending in a zero, especially as marked by a landmark birthday. informal
See also: big
Farlex Partner Idioms Dictionary © Farlex 2017
See also: