When Joseph Smith originally organized the Relief Society, he said "that he would ordain them to preside over the Society..." (note: not to a priesthood office) but there's strong evidence that he used that word for lack of a better term. If you go to the Women's Exponent from September 1, 1880 vol. 9 no. 7 (I think page 53-54; it's in the Relief Society Reports section, just search for "reports"), it states:
"President Taylor having arrived and being invited to address the sisters … I understand that one of the objects of this meeting is the ordination of officers of the Relief Society who Were elected at our Conference held on Saturday June 19, 1880 at the Salt Lake Assembly Hall.
"On the occasion of the organization of the Relief Society by the Prophet Joseph Smith at Nauvoo, I was present. Sister Emma Smith was elected president and sisters Elizabeth Ann Whitney and Sarah M. Cleveland her Counselors. The Prophet Joseph then said that Sister Emma was named in the revelation recorded in the Book of Doctrine and Covenants concerning the Elect Lady and furthermore that she had been ordained to expound the Scriptures. By my request my Secretary Elder L. John Nuttall read to you relative to this meeting from the “Book of the Law of the Lord” at your Conference held June 19th, ult., which explained what was then done.
"The ordination then given did not mean the conferring of the Priesthood upon those sisters yet the sisters hold a portion of thq Priesthood in connection with their husbands. (Sisters Eliza R. Snow and Bathsheba W. Smith, stated that they so understood it in Nauvoo and have looked upon it always in that light.)
"As I stated, at that meeting, that I was called upon by the Prophet Joseph and I did then ordain Sisters Whitney and Cleveland, and blessed Sister Emma and set her apart. I could not ordain these sisters to anything more or to greater powers than had been conferred upon Sister Emma who had previously been ordained to expound the Scriptures, and that Joseph said at that time, that being an elect lady had its significance, and that the revelation was then fulfilled in Sister Emma being thus elected to preside of the Relief Society."
After reading that interesting part, I learned about how Emma actually felt about polygamy and later why the RS was discontinued for a time. These are always things I've wondered, but didn't have a primary source! Well, here they are! Right in The Woman's Exponent. Perhaps in a few years I can go read all the old issues. Maybe.
"However after this organization at Nauvoo, much disturbance arose among the sisters. I do not wish to be personal especially as Sister Emma is now dead, but think that some of those circumstances should be known. Sister Emma got severely tried in her mind about the doctrine of Plural Marriage and she made use of the position she held to try to pervert the minds of the sisters in relation to that doctrine. She tried to influence my first wife and to make her believe that the revelation was not correct. Sister Taylor was very much troubled thereat and asked me what it meant. Soon after, the prophet Joseph was in my house and I spoke to him in my wife's presence, in relation to what sister Emma had said, and Joseph replied, "Sister Emma would dethrone Jehovah to accomplish her purpose if she could." Some of you sisters are acquainted with what I refer to and of the prejudice that then existed.
"After the death of the Prophet Joseph, in consequence of the confusion then introduced, President B. Young thought it best to defer the operations of this organization---and the labors of the Society ceased, until he organized the sisters again here in this City.
"Those influences then introduced and then operating were not right, for the sisters in the various organization since have accomplished much good and should not be deprived of their rights and privileges because others have done wrong."
For more on the organization of the RS check out this Des News article by Eliza R. Snow.