probably
prolly
/ˈprɑli/Elision
In real speech
What happens to the sounds
The middle syllable -bab- drops out: probably → “PROL-ly”.
When to use it
Casual speech and texting. In formal writing use likely or most likely.
Casual → formal
Slang
prolly
Neutral
probably
Formal
most likely
Sound notes
Elision: a sound disappears completely (often t, v, h or th).