What's the difference between arpeggio and ostinato?

To my ignorant ear, they sound the same. I also use arpeggiator plugins with lots of variation options, possibly blurring the line between a simple up/downstairs note pattern (arpeggio?) into more dynamic expression, such as variable timing between notes (ostinato?). I know I could read up on the internet, but I want to hear it from fellow musicians.

AN arpeggio is a broken chord, so C Maj (C - E - G) will only be played from the notes of a chord in any direction (up, down, inside out etc), also an arp in synthesis terms can play through one, two or three octaves usually and at different note divisions etc.

AN Ostinato is a musical phrase or sequence which is not confined to a chord and has a melodic intention (doesn’t rely on a chord). A 303 riff is actually an Ostinato, An Ostinato could be C, F, A, C, E2 etc etc

On many occasions they can be exactly the same thing coincidentally. That’s how I interpret it anyways

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Ostinato is stubborn, repetitive… It is a rhythmic drawing based on the written chord / s that is repeated repeatedly, stubbornly. Normally, even though the chord changes, the rhythmic pattern of the ostinato remains the same

I like this question.

One more little nuance I’ll add to jjfagot’s excellent definition:

An ostinato creates tension & release by “pulling” away from harmonic context as it unrelentingly continues. The listener doesn’t mind because there is this sense that the context will change and “heal” the separation.

I think of pedal point (pedal tone) bass as being a similar device. A bass note is held/repeated as chords above it change-- creating a tension/release contour.

There could be such a thing as a bass ostinato (which may function as a pedal point thing). But I think it is fair to say that ostinato phrases most commonly happen in the upper or middle range.