bottleneck

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A narrow or obstructed section, as of a highway or a pipeline.
• noun A point or an area of traffic congestion.
• noun A hindrance to progress or production.
• noun The narrow part of a bottle near the top.
• noun Music A style of guitar playing in which an object, such as a piece of glass or metal, is passed across the strings to achieve a gliding sound.
• noun Biology An abrupt and severe reduction in the number of individuals during the history of a species of a population, often resulting in the loss of diversity from the gene pool.
• transitive verb To slow down or impede by creating an obstruction.

from the GNU version of the Collaborative International Dictionary of English.

• a location or situation in which otherwise rapid progress is impeded.
• a point at which road traffic slows due to congestion or narrowing of the roadway.
• an impasse.
• a narrowing.
• transitive verb same as obstruct.
• intransitive verb to become narrower as one approaches a point; -- said of roads.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The narrow portion that forms the pouring spout of a bottle; the neck of a bottle.
• noun In traffic, any narrowing of the road, especially resulting in a delay.
• noun Any delay; part of a process that is too slow or cumbersome.
• verb transitive To slow by causing a bottleneck.
• verb intransitive To form a bottleneck.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb slow down or impede by creating an obstruction
• noun the narrow part of a bottle near the top
• verb become narrow, like a bottleneck
• noun a narrowing that reduces the flow through a channel