*streig-

The core idea of this root was:

stroking, rubbing

The German source I am using (DWDS.de) says that it’s probably an extension of the root *ster- which was about spreading, stretching out (find more here: *ster(e)-) .

This would mean that besides streichen, also Strahl (ray), streifen (strip) and streuen (strew) would be part of this family, but the English sources I have seen do not mention this at all.

English family members are definitely related are strike, stroke, stripe and streak.