What ? Riddle

To a word of agreement, add one half of a fright;
Next subjoin what you never beheld in the night;
These rightly combined, you’ll quickly obtain;
What numbers have seen, but will not witness again.

Origin and Copyright Entities

I first found this at Smart-Kit, a very large collection of almost every riddle around. It inspired me to create this site, and I give all original credit for this to the submitter who submitted it to Smart-Kit. It resides here as a mere link for discussion. This riddle has thus transpired into public domain so reproduction here is fair and just. I provide a link to the Smart-Kit article, as a sign of thanks.

Hint

NOTE: The following sentences will start to reveal the above brain teasing riddle. If you do not want this added hint, do not continue reading. If you want to view the hint however, hover your mouse below:

Use each clause in the first two lines separately to aid in the discovery of the solution. Combine each sound together to form an end word (the associated image also bears a loose relationship to the solution. Still stuck? Begging for the answer? No matter, see it here.