Something horrid might be either detestable and/or scary, but it means extremely unpleasant, horrible, shocking, dreadful, etc.. It might be neither detestable or scary, as in, "The weather outside was horrid, with torrents of rain beating against the windows, but, inside, it was as warm and cozy as anyone could wish. In that case, you would have no reason to detest the weather or to be afraid.
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