Q: Is there a word category for a certain kind of words beginning with 'a-'? A few words beginning with an a came up to my mind recently because their structure is similar in the way they convey their meaning.
Those words are like: atop, alight; afloat, afresh, anew, asleep, etc.
Where a seems to have a meaning like "on the _ of", "in the _ of", "on a", "in a" or other particular meanings that slightly change the meaning of the following syllable.
Though these words obviously do not belong to the same part of speech, are they all linked? Also, why is the prefix "a" so common?

A: Michael Quinion, Ologies and Isms: Word Beginnings and Endings (2002) offers a useful summary of the origin and application of this type of a- prefix:

a- Towards, of, in, into, or at; marking some ongoing process or state; movement onwards or away. {Old English prepositions of or on (sometimes as unstressed an), or the Old English prefix a-.}
The Old English prepositions were originally separate words, but became reduced to a- and attached to the words they once modified. The process can be seen in alive, which in Old English was two words, on life, literally 'in life'; others of similar type are aside, akin, and anew. Some examples are verbs derived from Old English a-, which had an idea about it of an action or an intensification of an action: arise, abide, and awake.
Some adjectives imply a continuing or active state, and have much the same force as a present participle ending in -ing: ablaze, abuzz, afire, afoot, aglow, astride. Others combine the prefix with a present participle, usually hyphenated; such words imply an ongoing process or activity: a-brewing, a-roving, a-hunting, a-wasting; though they are mostly now archaic, literary, or dialectal, the form has had a small revival in recent decades, as in Bob Dylan's song lyric The times they are a-changing.

So we have a prefix form that may appear in nouns (e.g., aside), verbs (e.g., arise), adjectives (e.g., aplenty), adverbs (e.g., apart), or prepositions (e.g., above) and may indicate, variously, movement in a particular direction, intensification, or ongoingness. And as if this multipurpose utility weren't complicated enough, an entirely separate prefix a- (originating in the Greek negation prefix α-) attaches to many English words with the meaning "not."

A: I believe "a" is short for "at".
A long time ago someone could have said "Alfred is at sleep."
