This is the 2908th most frequent Japanese word.
やろ
"やろ" is a casual Kansai dialect expression meaning "probably," "I guess," or "isn't it?" depending on context.
The word 'だろう' in this sentence is a form of 'やろ', used to express a probability or expectation.
明日は雨が降るだろう。
It will probably rain tomorrow.
Here, 'やろう' derived from 'やろ' indicates an inferred expectation.
彼が遅刻するやろうと思っていた。
I thought he would likely be late.
In this sentence, 'やろ?' is used as a casual confirmation question, asking if the stated assumption is true.