conjunction
Colloquial contraction of それで, used in casual speech to connect clauses with a meaning like 'and then', 'so', or 'because of that'.
See also: それで
昨日は雨が降った。そんで、試合は中止になった。
It rained yesterday. And so the game was canceled.
そんで、どうしたの?
So, what happened?