“a-” (a with a hyphen) is not a single fixed word in English, but it’s commonly used as a prefix or abbreviation marker.

Main meanings depend on context:

• Prefix form (rare in modern English alone):
  It can indicate “without” or “lacking” in older/technical usage (from Greek a- meaning “not”).
  • Example: asymmetrical originally comes from a- + symmetrical.
• Abbreviation / grading:
  • In school grading, A- means slightly below an A grade.
• Stylistic/linguistic fragment:
  Sometimes used in notes, coding, or lists to indicate a labeled item starting with “a”.

In short: “a-” is usually a prefix marker or shorthand, not a standalone word.