Petrichor
From Tardis Wiki, the free Doctor Who reference
Petrichor was, as defined by Idris, the smell of dust after rain. Idris used the word "Petrichor" as part of the key to open a back-up TARDIS control, which she gave to Rory through a telepathic link. (DW: The Doctor's Wife)
Petrichor was also the name of a fragrance for which Amy Pond posed as a model in an advertisement. Its slogan was "For the girl who's tired of waiting." This modelling job with Petrichor apparently made her rather famous. (DW: Closing Time)
Real world
The word "petrichor" was coined in 1964 in an article published in the magazine Nature. This means a word used as a major plot element in a Doctor Who episode did not actually exist when Doctor Who first went on the air in 1963.
