Having just got home from work I dived for my Oxford Dictionary of music. Never fails me....
HEMIOLA or HEMIOLIA. The rhythmic devide of superimposing two notes in the time of three, or three in the time of two.
3 x. x. |x. x. |x. x. |x. x. |
4 x x x|x x x|x x x|x x x |
Those two lines are supposed to be played at the same time, couldn;t get them to line up properly!
So I guess I was a bit wrong after all. Sorry!
No idea what the term was I was talking about in that case. Will have to try to find it to save a bit of face! lol