Do not behave like that woman who had spun her yarn strongly – [be not like this by] using your oaths as a means of deceiving one another, simply because some of you may be more powerful than others. By all this, Allah but puts you to a test – and [He does it] so that on the Day of Judgment He will certainly reveal to you the truth about which you differed.
Meaning:-
spins her yarn: If you say that someone spins a yarn, you mean that they tell a story that is not true, often an interesting or imaginative one.
Spun: Spun is having twisted.
Yarn: tell a long or implausible story.