This is the best definition of the word "placidly." In this passage, we learn of a woman who was knitting "placidly." This means that she was knitting in a way that seemed relaxed and calm, and that she appeared to be enjoying her task. When you are unable to look up the meaning of a word in a dictionary, it is useful to look at the context that surrounds the word, as this can give you an indication of the most likely meaning of the word.
