1. From Old English "on-" or "an-": This prefix indicates "on", "in", or "at". It's found in words like:
* abroad: "on broad"
* asleep: "in sleep"
* around: "on round"
2. From Latin "ad-": This prefix means "to", "toward", or "at". It's found in words like:
* arrive: "to arrive"
* attend: "to tend to"
* admit: "to let in"
3. From Greek "an-": This prefix means "without", "not", or "lack of". It's found in words like:
* amorphous: "without form"
* anarchy: "without rule"
* anonymous: "without a name"
4. From French "à" : This prefix means "to" or "at". It's found in words like:
* apropos: "to the point"
* adieu: "to God"
It's important to note that the prefix "a-" can sometimes be combined with other prefixes to form more complex words. For example, the word "abnormal" combines "ab-" (from Latin "ab", meaning "away from") with "normal".
In some cases, the exact origin of "a-" may be difficult to trace, as the word may have evolved over time.