See note s.v. h_ interj.
The suggestion that this word means "since" in LS2 is yet another somewhat astounding example of poor lexicography. The entire phrase ܗܐ ܡܢ ܕ means "now since" to be sure, but the "since" part comes from ܡܢ ܕ not from ܗܐ, while our word still means what it means.