How to delete (not cut) in Vim?

How can I delete a line without putting it into my default buffer?

Example:

line that will be copied.line that I want to be substitued with the previous one.

What I'm trying to do:

yyddp

But Vim replaces the recent copied string with the deleted (cutted) one. I know that I can use buffers like, "1yy, dd then "1p, but I always forget to put the copied string in a buffer then I need to paste my contents first (line that will be copied) and then delete what I want (line that I want to be substituted with the previous one.)

How can I really delete a text in Vi(m) without copying it?

Another related question is how I can forward delete a word in insert mode? I want something similar to Ctrl+w.