If you’ve ever spotted somebody wriggling and being evasive, trying to avoid giving a straight answer to a straight question, then you have observed tergiversation.
The Romans observed this phenomenon as often as we do, and already had the word for it, tergiversari, to turn one’s back, shuffle, or practise evasion, from tergum, back, and vertere, to turn. One of its English senses, in older dictionaries often given as the main one, is of a deserter from a party, a renegade or apostate.
An example in that sense appeared in Blackwood’s Magazine in 1831: “ ‘I am liberal in my politics’, says some twenty-times tergiversated turncoat”. Dickens seems to be using it in the more modern sense in A Tale of Two Cities: “He knew ... that flight was impossible; that he was tied fast under the shadow of the axe; and that in spite of his utmost tergiversation and treachery in furtherance of the reigning terror, a word might bring it down upon him”.
As those who tergiversate in either sense usually show similar symptoms of ducking and weaving, as John Barsad was doing in Dickens’s book, the link between the two senses is clear enough, and in fact it’s sometimes difficult to decide which sense was meant. The turncoat sense is still sometimes encountered, but the main one is now of someone trying to weasel out of an untenable position.