grue

To expand, an object is grue if green and examined before time t, or blue and not examined before t.

'It is pitch black. You are likely to be eaten by a grue.' (Zork)

Also a creation of Nelson Goodman. See also bleen.

The noise made by people feeling ill in children's comics in the 80's.

EDIT: ignore the above! The word I was thinking of was the homonym groo.