The NIV has the term ‘deaconnesses’ in the footnotes. Biblically is there
such a thing as a deaconness and what would their role be if there is?

There are two questions implied here. One is whether there is such a thing
as a deaconess, and the other is whether this is implied by the Bible. I
assume you refer to 1 Timothy 3:11. “In the same way, their wives
(footnote deaconesses in the NIV) are to be women worthy of respect…
Having looked this passage up in my Greek interlinear, the word used in 1
Timothy is definitely wives, not deaconesses. The word for deacons in the
Greek is, in transliteration, diakonos. Diakonos means literally servant.
This word is definitely not used in 1 Timothy 3:11. Therefore, the simple
answer to your question is no, there is no such thing as a biblically
defined position of deaconess.

Having said that, if the church chose to call the wives of deacons
deaconesses, I do not suppose this would be wrong. In fact, if the local
eldership chose to appoint women who were well qualified to serve the
church in special positions and called them deaconesses, even if their
husbands were not deacons, I suppose there would be nothing wrong with
that either. What one can say is that in this case, it should be
remembered that this would be a tradition, rather than a biblically
designated position in the church. It is wise for the New Testament Church
to remind itself which of its practices are biblical and which are human
creations as a matter of expediency.

John Oakes, PhD