I don't want to prolong this thread as it is on the wrong board.

From all the responses I have received, some off the board, I gather the history is something like this (almost as fun as genealogy).

The original events were time trials for motor cars.
A cup, trophy, was established for cars in the 'tourist' class who competed over the mountain course.

This became known as "The TT Course".

Soon events were established for motor cycles using the same course.

The motor cycle events were and are time trials in that riders start at spaced intervals and the rider with the shortest overall time is the winner.

My comment re Le Mans start applied only to the car races and was sparked by a vague memory of the car events post WWII. A Prince Beira figures in those memories.

Anyway, thanks again to everyone. TT = Tourist Trophy which is what I always believed but wanted confirmed.