the whole nine yards

Dave Wilton summarises the findings of Bonnie Taylor-Blake and others:[1]

The phrase doesn’t have one particular origin, nor does it represent one particular metaphor. Instead, it seems to have evolved from a sense of yard meaning a vague quantity of something. Later, the words full or whole were attached to it, and even later it was quantified by the numbers six and nine, with the whole nine yards eventually winning out and becoming the canonical form. Use of the full phrase was for a long time restricted to the American Midwest, in particular to the region around the Kentucky-Indiana border, before breaking out into general American parlance in the middle of the twentieth century. [...]

So regardless of what someone else has told you, the whole nine yards does not refer to the length of a belt of WWII machine-gun ammunition, the amount of material needed to make a Scottish kilt, the number of spars on a sailing ship, the amount of concrete a cement mixer holds, or anything else.

the whole nine yards

1. All the way; with everything done completely or thoroughly.
   • 2007, Thomas Mchenry, Along the Rails: A Juror's Journey‎, page 85:

     Would they want me to vote my conscience or would they want us to unanimously go the whole nine yards, declare him sane and possibly have the trial end up in a death sentence?

   • 2007, R. D. Reynolds, The Wrestlecrap Book of Lists!‎, page 18:

     WWE went the whole nine yards, from making Tshirts with the slogan to having announcers mention his new handle approximately every four seconds anytime he was on-screen.

   • 2012, Susan Stephens, Working with the Enemy‎, page 164:

     Colleen had gone the whole nine yards, dressing up as a fortune teller, complete with huge gold earrings and a headscarf, which she'd plucked from her normal accessory box, she told Bronte.

the whole nine yards

1. (And) everything; often used, like etc., to finish out a list.
   • 1908 June 4, The Mitchell Commercial‎, Lawrence County, Indiana, retrieved 14 August 2018, page 3, col.5:

     While there Roscoe went fishing and has a big story to tell, but we refuse to stand while he unloads. He will catch some unsuspecting individual some of these days and give him the whole nine yards.

   • 2002, Mary Losure, Our Way Or the Highway: Inside the Minnehaha Free State‎, page 161:

     "I had a good job, a nice little house, the whole nine yards," she said.

   • 2009, Jason Barbacovi, Me and Chairman Mao‎, page 101:

     No, to her credit she kept right on going the whole time, telling me how she was from Mongolia, how she was an art student, how she was having an exhibition — the whole nine yards.

   • 2009, Reynaldo Laureano, Politics Vs. Prejudice in the Highway Patrol‎, page 46:

     Mario asked me to explain to him the whole nine yards so I decided to start off on a good note.

• (other "whole ___" terms that mean "everything / the whole thing"): whole package, whole shebang, whole ball of wax, whole enchilada, whole kit and caboodle, whole shooting match, whole shitting match, whole smash
  • whole hog, go the whole hog
  • the whole world, the whole world and his dog