Antonyms of rigidly:
imprecisely, inexactly, loosely.
Examples of usage:
  1. Straightening her back and head against the tree, she clasped her hands rigidly on her knee.
    "The Mating of Lydia", Mrs. Humphry Ward.
  2. At first Marta listened rigidly, but as the narrative proceeded her interest grew.
    "The Last Shot", Frederick Palmer.
  3. After the accusation fell from the foreman's lips, I quite suddenly became aware of the fact that she was standing rigidly erect, one hand strained to her bosom, the other clenched tightly against her cheek.
    "The Paternoster Ruby", Charles Edmonds Walk.