Which means......

.....A woman who wants to improve the life and chances of women and girls locally and inter-nationally - and enjoys doing so with like-minded women. 

The word comes from the Latin soror meaning sister and optima meaning best. There are 3000 clubs in over 100 countries - all involved in projects big and small, that combined make a difference. 

The local website told me more. Worth looking into....
www.sigi.org/bromley

 I came across this new word this evening when we took a stroll down to a Christmas Tree Festival at a local church and this organisation had decorated a tree. Lots of other organisations represented too and in very original ways. All trees had to be "real" so the festival last just a week ...before the needles start falling I suppose. I shall go back for another browse.