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1.
Another name for the pairing Thor and Loki. Often it describes a romantic/sexual relationship, but isn't limited to.
Martha liked to imagine Thor and Loki kissing passionately, she was a thunderfrost fan.
by Just another shipper August 04, 2012
 
2.
The name given to the slash pairing between the adopted brothers Thor Odinson and Loki Laufeyson, originally characters from Norse mythology, but now usually related to the Marvel comics and more recently the movies 'Thor' and 'The Avengers'.

The name relates to the fact that Thor is the god of thunder and Loki is the son of the frost giant Laufey.
The terms is used mostly among fangirls on Tumblr. Another name for Thunderfrost is Thorki.
1. Fangirl on Tumblr: OMG Thunderfrost is giving me SO MANY FEELINGS adghslajvhafgsfdja

2. Other fangirl on Tumblr: Hey, have you seen this sweet new Thunderfrost fanart? They're so perfect together!
by Leavinghome June 01, 2012