
I lost that KEY chain years ago.
The Big Bang Theory Season 11, Episode 9

I was writing an e-mail
and the A KEY got stuck.
The Big Bang Theory Season 1, Episode 13

Sansa is the KEY to the North? I seem to
remember she has an older brother.
Game of Thrones Season 3, Episode 5

Apparently,
a KEY component
The Big Bang Theory Season 7, Episode 12

So, the KEY is
The Big Bang Theory Season 10, Episode 22