bottleneck

The narrow portion that forms the pouring spout of a bottle; the neck of a bottle.

In traffic, any narrowing of the road, especially resulting in a delay.

(by extension) The part of a process that is too slow or cumbersome.

“It is easy to create entries; processing the paperwork is the bottleneck.”

To slow by causing a bottleneck.

“The merge bottlenecked the traffic every morning.”

To form a bottleneck.

“The traffic bottlenecked at the merge every morning.”