Big Difference
noun
違い is difference, so a big one of those is a big difference.
The reading is 違う plus 大 of 大きい (おお) put together. You can remember this because when you see the difference (the BIG difference), you say "oohhhhh" (お), because you were surprised you didn't see it before.
堅い木の椅子と柔らかい快適な椅子じゃあ大違いだよ。
There is a big difference between a hard wooden chair and a soft cushy chair.