by Mark Israel
     [This is a fast-access FAQ excerpt.]
The conjunction "till" is not a shortening of "until".  MWCD10
dates "till" from the 12th century and "until" from the 13th century.
"Until" was a compound, whose first element also survives in "unto",
and whose second element was the ancestor of "till".
   The spelling "'til" occurs, but is not standard anywhere.