"wholly, entirely, completely," early 13c., altogedere, a strengthened form of all (also see together); used in the sense of "a whole" from 1660s. OED notes, "There is a common tendency to write altogether where all together is logically preferable," and gives examples from 1765. The altogether "a condition of nakedness" is from 1894.
altogether he earns close to a million dollars
altogether, I'm sorry it happened
an altogether new approach
it was not altogether her fault
in the altogether
alti-
altimeter
altimetry
altitude
alto
altogether
alto-rilievo
altruism
altruist
altruistic
alum