A-
Prefix very much employed in medicine and all of the health sciences, indicating 'not, without, -less' as, for example, in alexia (not read), aphagia (not eat), aphonia (not voice, voiceless).
The 'a-' usually becomes 'an-' before a vowel as, for example, in anemia (without blood), anophthalmia (no eye), anotia (no ear), anoxia (no oxygen).
The prefix 'a-' comes from the Greek meaning 'not.'