1. (noun)angstrom, angstrom unit, A a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation Synonyms: antiophthalmic factor, adenine, axerophthol, vitamin A, group A, ampere, angstrom, angstrom unit, deoxyadenosine monophosphate, amp, type A