grundies

• As Grundies, an underwear brand name.
• Possibly an abbreviated form of Reg Grundies, rhyming slang for undies, after media magnate Reg Grundy.

• Audio (General Australian):

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grundies pl (plural only)

1. (Australia, New Zealand, UK, slang) Underpants.
   • 2003, Ken Catran, Bloody Liggie‎^[1], page 95:

     So I shrugged and shifted like my grundies were too tight.

“grundies”, in Collins English Dictionary.

grundiēs

1. second-person singular future active indicative of grundiō