I just finished the movie "Raise the Red Lantern" 【大红灯笼高高挂】with my girlfriend, and she asked me about the etymology of "太太” as lady, wife, mistress, etc. Given the rather simple nature of the character and the individual definition of 太 having nothing to do with wife/lady, I have found it difficult to figure out. How did the reduplicated "太太“ come to mean wife or lady?
There are different theories, one said it came from 太皇太后 (A queen who became the Emperor's grandmother), but I seriously doubt it to be the case. From a nickname/ honorific for the Emperor's grandmother to an honorific for someone's wife is a big stretch.
The following is more believable to me.
According to this article 为何人们把已婚的女性称为“太太”？原来有“太太”这么好的寓意
周朝有三位开国先君，而这三位先王的夫人，也就是太王的夫人太姜、季历的夫人太任、文王的夫人太姒 ，都母仪天下，辅佐和教化了开万世太平的君王。 这三位夫人，被称为周初“三太”
There were three founding kings of the Zhou Dynasty, and the wives of these three kings, namely, the wife of King Tai (太王), Tai Jiang (太姜), the wife of King Ji Li (季历), Tai Ren (太任), and the wife of King Wen (文王), Tai Si (太姒).
All of them were great wives who assisted a king. These three ladies were called "The Three Tais (三太)" of the early Zhou Dynasty
High society circle started to use 太太 as an honorific for one's wife (praising her for as good a wife as the 三太). Eventually, the common people started to use 太太 as an honorific for any married woman as well.
“太太”, used as a honorific term for wife, was medntioned in “甲乙剩言”, and was quoted in “全閩詩話” volume 8:
only wife of higher ranking officials (中丞以上) could be called “太太”; afterwards, this term was “deflated”, that it’s used as a term for wife.
it existed not earlier than ming dynasty.