subs. (old).1. A counterfeit sovereign: YOUNG ILLEGITIMATE = a half sovereign.BEE (1823).
2. (common).A low grade costermonger.
Adj. (racing).Applied to steeple-chasing or hurdle-racing, as distinguished from work on the flat.
1888. Daily Chronicle, 31 Oct. A much smarter performer at the ILLEGITIMATE game than she was on the flat.