An-: Prefix very much employed in medicine and all of the health sciences, indicating "not, without, or -less."
For example, the prefix "an" figures into these words: anemia (without blood), anophthalmia (no eye), anotia (no ear), anoxia (no oxygen).
The "an-" usually becomes "a-" before a consonant as, for example, in alexia (not read), aphagia (not eat), aphonia (not voice, voiceless).
The prefix "an-" comes from the Greek meaning "not."
