The proper way to abbreviate approximate when writing a date is with the Latin word circa, rather than approx.
The abbreviation of approximate is approx.
The only opposite of abbreviation is writing out, or expanding the abbreviation.
Abbreviation
The abbreviation form of writing Emmanuel may be Manu or Manuel.
The abbreviation for years commonly used in formal writing and documentation is "yr."
"There'd" is the abbreviation for "there would," but I would be careful not to use it in formal writing.
An abbreviation is a way to shorten a longer word in order to save space when writing. There is no current abbreviation for impressionism.
The approximate date of conception was September 22nd 2009
A "circa date" is an approximate date used when the exact date of an event is not known.
I believe you are thinking of "abbreviation".
The abbreviation of Maine is ME.
That would be Sra.