Ellipse & Ellipsis

 -se – an oval.
-sis – an omission.

Not actually homophones, and I wonder how often they'd be used incorrectly in writing. But I sure hear people mix them up in conversation, just like Climactic/Climatic.

Parity & Parody

 -ity – a state of fairness, equality.
-ody – a humorously exaggerated imitation.