depreciate

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

• intransitive verb To lessen the price or value of.
• intransitive verb To write off an expenditure for (a tangible asset) by prorating over a certain period, usually the estimated useful life of the asset.
• intransitive verb To think or speak of as being of little worth; belittle. synonym: disparage.
• intransitive verb To diminish in price or value.

from The Century Dictionary.

• To lessen the value of; bring down in value or rate: as, to depreciate goods or prices; to depreciate railroad stocks.
• To undervalue or underrate; represent as of little value or merit, or of less than is commonly supposed; belittle.
• Synonyms To lower.
• Disparage, Detract from, etc. (see decry); to traduce, underrate, slur.
• To fall in value; become of less worth: as, a paper currency will depreciate unless it is convertible into specie; real estate is depreciating.

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

• intransitive verb To fall in value; to become of less worth; to sink in estimation.
• transitive verb To lessen in price or estimated value; to lower the worth of; to represent as of little value or claim to esteem; to undervalue.

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

• verb intransitive To reduce in value over time.
• verb transitive To belittle

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

• verb belittle
• verb lower the value of something
• verb lose in value