What he got by way of a settlement was a pittance.

The word 'pittance' means a very small or inadequate amount of money. Petty amount and miniscule amount directly mean a small amount, matching pittance. An instalment can also refer to a small portion paid. However, 'bonanza' means a sudden large amount of wealth or good fortune, which is the exact opposite of pittance. Therefore, bonanza is the odd one out.