Recent versions of media-fonts/terminus include a USE flag called "center-tilda" whose description is: Place the '~' character vertically centered on the line instead of to the top. The name of this symbol, '~', is written "tilde" in English. The USE flag should therefore be called "center-tilde".
Whoops, that should have said "media-fonts/terminus-font". Skitt's law shows its face again.
Fixed. Thanks for reporting!