bottleneck

(noun) a narrowing that reduces the flow through a channel. Synonyms: constriction, chokepoint.

(noun) the narrow part of a bottle near the top.

(verb) slow down or impede by creating an obstruction. Example: "His laziness has bottlenecked our efforts to reform the system."

(verb) become narrow, like a bottleneck. Example: "Right by the bridge, the road bottlenecks."