Thank you Vinod. After my original mistake I compounded it after successfully finding Safari when I opened Trash, by trying to move it to the dock, over the original icon, which was still in place, even though it was not working. Much later I discovered by googling that I should move the icon into applications.
By the time I discovered this fact had mislaid the icon; I think I may have simply accidentally moved it up in the trash when I tried to move the icon as above, and really thought I had made it disappear completely from the screen, leaving only the useless icon in the dock.
Somehow or other when floundering about I discovered that the icon was actually still in trash; I had not realised that I could scroll the trash screen which I had opened, until I flicked it up by accident.
By that time I had read something else about it, which said do not try to move the icon from trash back to the dock, but into Applications. I did so and Voila! I am back in business, crisis finally over.
Thank you very much for your help, and I have also learned a little bit more about my computer. Carol