It is called atari 当たり.
The word is connected to the verb ataru 当たる.
Which indeed can mean to hit, to meet, to collide, to touch, to clash.
Compare atemi 当て身.
You move the partner using "the point at which the ki collides". (see 0:40)
I understand the meaning of atari.
Just like I understand the meaning of musubi.
I am trying to figure out whether you think this is something specific for Aikido or for a specific style of Aikido or for Endo shihan, whether or not there is a difference for you between musubi and "blending". Your comment to Mary Eastland's post suggests that you have a different view on this, yet you do not explain the counterargument. The video itself does not help to clarify the counter argument. Perhaps you care to elaborate?