incompatible

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

• adjective Not capable of existing in agreement or harmony with something else.
• adjective Not capable of living or working together happily or harmoniously; antagonistic.
• adjective Impossible to be held simultaneously by one person.
• adjective Logic That cannot be simultaneously true; mutually exclusive.
• adjective Producing an undesirable effect when used in combination with a particular substance.
• adjective Not immunologically compatible.
• noun One that is incompatible.

from The Century Dictionary.

• Not compatible; incapable of harmonizing or agreeing; mutually repelling; incongruous.
• Specifically That cannot coexist or be conjoined, as mutually repellent substances, or ingredients in a medicine which react on each other, causing precipitation or serious change of composition, or remedies which have opposite medicinal properties. Such substances are distinctively called incompatibles.
• Persons or things that are incompatible with each other. See I., 2.

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

• adjective Not compatible; so differing as to be incapable of harmonious combination or coexistence; inconsistent in thought or being; irreconcilably disagreeing
• adjective (Chem.) Incapable of being together without mutual reaction or decomposition, as certain medicines.
• adjective (Logic) terms which can not be combined in thought.
• noun (Med. & Chem.) An incompatible substance; esp., in pl., things which can not be placed or used together because of a change of chemical composition or of opposing medicinal qualities.

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

• adjective Of two things: impossible to coexist; not congruous because of differences; irreconcilable; disagreeing.
• noun medicine, chemistry An incompatible substance; one of a group of things that cannot be placed or used together because of a change of chemical composition or opposing medicinal qualities.

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

• adjective incapable of being used with or connected to other devices or components without modification
• adjective not compatible
• adjective not easy to combine harmoniously
• adjective used especially of solids or solutions; incapable of blending into a stable homogeneous mixture
• adjective not in keeping with what is correct or proper
• adjective used especially of drugs or muscles that counteract or neutralize each other's effect
• adjective not compatible with other facts
• adjective not suitable to your tastes or needs
• adjective of words so related that one contrasts with the other