Atonce or Attonce: How To spell?
The word Atonce is misspelled against Attonce, an adverb meaning "At once; together."
Attonce has double "tt" is mispronounced as "t"Remember double 'TT' in between the strings a & once which should not be misspelled with single 'T'
Wrong Spelling:  a-t-once  Correct Spelling:  a-tt-once 
Find more incorrect spellings of Attonce to spell right way.