Select Word Under Cursor in Ex mode in Vim

Search and Replacement is one of the most powerful feature in Vim. I use singular here because I consider "Search and Replacement" is one word, why not? You only need couple key strokes to search the word under the cursor.

:        => in Ex mode
<C-r> => Control + r
<C-w> => Control + w
Help :h <c-w> or CTRL-r