a- Definition

a-¹
prefix

1. Signifying to or towards.

Example: ashore
2. Signifying in the process or state of something.

Example: abuzz
Example: a-roving
3. Signifying on.

Example: afire
4. Signifying in.

Example: asleep

Etymology: Anglo-Saxon an, originally a preposition; sense 2 is still productive.

---

a-²
an-
prefix

1. Signifying not; without; opposite to.

Example: amoral
Example: ahistorical
Example: anaemia
Example: anhydrous

Etymology: Greek.