title of respect, 1520s, from Spanish or Portuguese Don, a title of respect prefixed to a man's Christian name, from Latin dominus "lord, master, owner" (from domus "house," from PIE root *dem- "house, household").
It took on a general sense of "person of high importance or leading position," hence the English university sense "fellow of a college, any college authority" (c. 1660), originally student slang. The underworld sense is by 1952, from Italian don. The fem. form is Portuguese Dona, Spanish Doña, Italian Donna.
"to put on (articles of clothing)," mid-14c. contraction of do on (compare doff). "After 1650 retained in popular use only in north. dialect; as a literary archaism it has become very frequent in 19th c." [OED]. Related: Donned; donning.