a-, an-

(Greek: prefix; no, absence of, without, lack of; not)

These prefixes are normally used with elements of Greek origin, a- is used before consonants and an- is used before vowels.

It affects the meanings of hundreds of words.

There are too many words that use these prefix elements to list all of them on this site; however, there are significant examples listed in this and the other units where they exist.

avascular (adjective), more avascular, most avascular
Lacking in blood vessels or having a poor blood supply: Avascular necrosis is the death of body tissue because the blood supply has been cut off.

Dr. MacSween told Ralph that the avascular blood vessels and other tissues in his body were unable to provide sufficient blood to his bones and other body organs.

Some plants can also have avascular systems which are not able to carry sufficient water and nutrients throughout their systems.

avascular necrosis (s) (noun), avascular necroses (pl)
Dead bone tissue because of an impaired or disrupted blood supply: One kind of avascular necrosis is that which is caused by a traumatic injury or disease and it is marked by severe pain in the affected region and by weakened bone (osteonecrosis) that may flatten and collapse.
avascularity (s) (noun), avascularities (pl)
A condition in which the body has few or no blood vessels: The medics were concerned about Terence's avascularity because blood was not being supplied to the organs of his body.
avascularization (s) (noun), avascularizations (pl)
The expulsion or diversion of blood from a body part by means of a tourniquet or an arterial compression: The doctors used avascularization to keep the blood flow away from the organ they were about to operate on by using compression or pressing certain body parts together.
avirulence (s) (noun), avirulences (pl)
That which is not a serious disease nor a disease-causing agent: Dr. Nickerson told Mrs. O'Donnell's family that her illness could be considered virulence; that is, it was not highly infectious, not malignant, and not deadly.
axenic (adjective), more axenic, most axenic
Characterized by not being contaminated by or associated with other foreign organisms: There are supposedly some axenic cultures of microorganisms that exist without the presence of other organisms.

Some experimental animals are raised in axenic conditions so they can be used for special research projects.

azoic (adjective), more azoic, most azoic
A reference to being devoid of living organisms; without life: Biologists talk about an azoic time when our Earth existed without any life on it.

Specifically, designating the Early Precambrian ("Archean") era, before life appeared on earth because the azoic rocks did not contain any signs of organic remains.

azoospermia (s) (noun), azoospermias (pl)
Absence of living spermatozoa in the semen: Infertility, but not impotence, is associated with azoospermia.
azygous, azygos (adjective); more azygous, more azygos; most azygous, most azygos
1. A reference to occurring singly; not occurring as one of a pair; such as, a vein or muscle: The medical students learned that the superior vena cava (one of two very large veins) receives blood from the azygous vein, which drains blood from the chest.

The physicians examined Richard's azygos veins to make sure that the three unpaired veins of the abdomen and thorax emptied properly into the inferior vena cave.

2. Etymology: from Greek meaning "unyoked" or "not a pair"; from a-, "without" + zygon, "a yoke".
tactile amnesia (s) (noun), tactile amnesias (pl)
The loss or the lack of the ability to understand the form and nature of objects that are touched (stereognosis), a form of tactile agnosia: Tactile amnesia is the loss of the ability to determine the shape of objects when touching them.