1 totally, completely (you are altogether wrong).
2 on the whole (altogether it had been a good day).
3 in total (there are six bedrooms altogether).
Usage:
Note that all together is used to mean 'all at once' or 'all in one place', as in there are six bedrooms all together.
Phrases and idioms:
in the altogether colloq. naked.
Etymology: ME f. ALL + TOGETHER
Useful english dictionary. 2012.