Can a Bow (Weapon) be strung with a Guitar string?

Not realistically. Most bowstrings have a tensile strength between 4–8 times the rated draw strength of the bow, so the string on a 60 lb. bow would have a breaking strength of at least 240 lbs. The tension on the 6th (E) string of an acoustic guitar is only around 18 lbs. It can take a bit more tension than that, but not 13 times more.

You NEVER want to come in contact with the string when released. No matter what string you use it will cause damage to an unprotected arm.
@thorninmud has the right idea. Tensile strength is the determining factor.

No. a friend of mine tried it about 40 years ago. He was using a the string snapped when he tried to draw it. @thorninmud confirms by figures what observed first-hand.

He actually used a bass guitar .105 inch wound steel string, which had been rescued when a bassist friend had changed strings on his instrument.

@Yetanotheruser – If your friend still has both eyes, he should be thanking his lucky stars.

We were quite the adventurers back then…Oh, the stories I could tell. Neither he or I sustained any damage (we had survived many other adventures). He passed about ten years ago of totally unrelated causes.

Yes if the guitar strings were made of catgut (Cattle intestines). I’d wind about 5 or six catgut strings tightly around each other and wear a full face and arm shields when testing it.