The American Heritage® Dictionary of the English Language, 4th Edition
n. The state, quality, sense, or fact of being near or next; closeness: "Swift's major writings have a proximity and a relevance that is splendidly invigorating” ( M.D. Aeschliman). See Usage Note at redundancy.
n. closeness; the state of being near as in space, time, or relationship.
the GNU version of the Collaborative International Dictionary of English
n. The quality or state of being next in time, place, causation, influence, etc.; immediate nearness, either in place, blood, or alliance.
The Century Dictionary and Cyclopedia
n. The state of being proximate; nearness in place, time, or relation.
n.Synonyms Vicinity, etc. (see neighborhood), adjacency.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a Gestalt principle of organization holding that (other things being equal) objects or events that are near to one another (in space or time) are perceived as belonging together as a unit
n. the property of being close together
n. the region close around a person or thing
Word Usage
"Assuming each person incurs a slight cost when an additional rider gets on a bus (inaccurate, as the cost is only truly incurred by those in proximity to the new rider) the average cost is still minimized by cramming people in as opposed to making some wait."