Piteous means 'likely to excite pity'
Pitiable means 'deserving pity'.
Pitiful means compassionate or calling for pity,even contemptible.
1. At the piteous cry of the calf,the mother cow rushed to its rescue.
2. A piteous sight.
1. The condition of the peasants in India is pitiable.
2. He made a pitiable attempt.
1. He shows a pitiful lack of understanding.
2. A pitiful amount of money.