complication

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

• noun The act of complicating.
• noun A confused or intricate relationship of parts.
• noun A factor, condition, or element that complicates.
• noun Medicine A secondary disease, an accident, or a negative reaction occurring during the course of an illness and usually aggravating the illness.

from The Century Dictionary.

• noun In psychology, the simultaneous association of perceptions or ideas of different senses.
• noun A complex combination or intricate intermingling of things, parts, elements, etc.; especially, a perplexing or incongruous intermixture or combination; a confused complex or complexity: as, a complication of knots in a rope; a complication of ideas, diseases, or misfortunes; the complication of one's affairs with those of another.
• noun That which renders complex, involved, or intricate; that which causes difficulty, entanglement, or interference; an involved and troublesome or embarrassing state of affairs.
• noun An entwining or infolding; an embrace.
• noun In entomology, the manner in which an insect folds its wings when at rest.
• noun In biology, a process the reverse of growth or development, by which the heterogeneous tends toward homogeneity.

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

• noun The act or process of complicating; the state of being complicated; intricate or confused relation of parts; entanglement; complexity.
• noun (Med.) A disease or diseases, or adventitious circumstances or conditions, coexistent with and modifying a primary disease, but not necessarily connected with it.

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

• noun The act or process of complicating; the state of being complicated; intricate or confused relation of parts; entanglement; complexity.
• noun A person who doesn't fit in with the main scheme of things; an interloper; someone you need to placate.
• noun medicine A disease or diseases, or adventitious circumstances or conditions, coexistent with and modifying a primary disease, but not necessarily connected with it.
• noun A feature beyond basic time display in a timepiece.

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

• noun puzzling complexity
• noun a situation or condition that is complex or confused
• noun any disease or disorder that occurs during the course of (or because of) another disease
• noun the act or process of complicating
• noun a development that complicates a situation