Nuns stay in the convent and are devoted to prayer, while deaconesses (and consecrated servants), live in the world, usually communally, and serve socially (more like post-vatican II RC nuns). This is a recent development. The order of deaconess had fallen into disuse and was revived.
Approximately when did this revival occur? Curious because when the subject of reviving 'deaconesses' comes up in EO circles, one of the points that regularly gets brought up is that St. Nectarios of Aegina ordained several deaconesses at the monastery he was spiritual father too. This was in 1911 or so. And as we have recently been informed, St. Nectarios was on very good terms with the Coptic Chuch while he was Metropolitan of Pentapolis.
I believe much more recently than that. http://weekly.ahram.org.eg/2000/479/spec1.htm
"Such regulations are enshrined in the Code for Consecrated Deaconesses, which was drawn up in 1992 by the Holy Synod, headed by Pope Shenouda III"
"a doctor who became a consecrated deaconess in 1980,"
Found it, http://www.bbc.co.uk/religion/religions/christianity/subdivisions/coptic_1.shtml
"The early Church had women deacons but abandoned this in the 13th century. The Church resumed the ordination of women as deaconesses in 1981 and there are now at least 400 consecrated deaconesses in the Coptic church. Traditionally, a deaconess is either a virgin or a widow."