Rust, the language designed by Graydon Hoare, was named after the Rust fungi. When asked why he chose the name Hoare said:
"I think I named it after fungi," said Hoare. "Rusts are amazing creatures. Five-lifecycle-phase heteroecious parasites [...] talk about over-engineered for survival.
He would also add that it was "a nice substring of 'robust'", as well as "trust", "frustrating", "rustic" and "thrust".
Sources: Chat thread