-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.
With an E – (v.) literally, to remove a fuse. Metaphorically, to make a situation less dangerous.
With an I and two Fs – (v.) to scatter or spread thinly.
(By the way, the adjective form of Diffuse has essentially the same meaning as the verb, but is pronounced with a hard S sound at the end, rather than the Z sound used here. Homographs!) :)
I thought this might be a good one for today since Tuesday is election day here in the US. Two homophones, and a third word thrown in for good measure. While "decent" isn't pronounced the same as the other two, it is easily confused on the page. So I thought it was a good idea to include it here.
Decent (DEE-sent) – good, kind, caring
Descent (di-SENT) – moving downward
Dissent (di-SENT) – protest