Here are a few examples of protean things.
Mammatus clouds, Photo by Derrich
photo of a drop of water by José Manuel Suárez
Photo of the god Zeus - well, a statue of him, anyway - by Jebulon
I could also add the symptoms of infection with HIV, but that's something for which I don't want to do an image search.
What do all these things have in common?
Can you work it out?
Well, they're all shape-shifters, or shape-changers, or they can appear in many different forms or guises.
So protean means liable to change shape, or appearing in different forms.
Thank heavens I've got that sorted out at last.
Spot the Frippet: something protean. Although the god Zeus was always changing shape (usually in order to seduce someone) it's another Greek mythical character, Proteus, who has given his name to the habit. Proteus was a sort of sea-shepherd who looked after Poseidon's sea-creatures and also had the gift of prophesy. This gift turned him into a huge celebrity, and so he started changing shape to avoid recognition.
The only way to get a selfie (or a prophesy) out of Proteus was to sneak up on him when he was asleep, and then hold onto him while he changed from one shape to another, until in the end he got fed up and told you what you wanted to know.