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.'