When my grandchildren were here earlier this month, it gave me the chance to hear new words that are being used in UK. When my granddaughter has a tantrum, her parents say she is having a strop.
The noun strop is derived from the adjective stroppy by a process we call back-formation. The more usual process of word-creation is derivation: you add a suffix on the end of a word to create a new word. So -y can be added to the noun wind to make the adjective windy, or cloud to make cloudy, or to sleep to make sleepy. But by the reverse process, you can take off what seems to be a suffix, which is why you can take the -y off the end of stroppy to create strop.
The process of back-formation has been around for some time, so donate was created by removing the -tion from donation, and edit was created from editor. I don't know if back-formation is becoming more common nowadays.
The other thing I don't know is how widespread the use of strop is. It might be just a coinage that is used by my son and his family.
