modify

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

• intransitive verb To change in form or character; alter.
• intransitive verb To make less extreme, severe, or strong.
• intransitive verb Grammar To qualify or limit the meaning of. For example, summer modifies day in the phrase a summer day.
• intransitive verb Linguistics To change (a vowel) by umlaut.
• intransitive verb To be or become modified; change.

from The Century Dictionary.

• To qualify; especially, to moderate or reduce in extent or degree.
• To change the properties, form, or function of; give a new form to; alter slightly or not very much; vary: as, to modify the terms of a contract; a prefix modifies the sense of a word; light is modified by its transmission through certain media.

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

• transitive verb To change somewhat the form or qualities of; to change a part of something while leaving most parts unchanged; to alter somewhat
• transitive verb To limit or reduce in extent or degree; to moderate; to qualify; to lower.

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

• verb transitive To make partial changes to.
• verb intransitive To be or become modified.

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

• verb add a modifier to a constituent
• verb make less severe or harsh or extreme
• verb cause to change; make different; cause a transformation