Wistful means having or showing a feeling of vague or regretful longing, especially accompanied by melancholy or sadness. It describes someone who is thoughtfully sad because of unfulfilled desires or nostalgic memories. Options A, B, and C are unrelated meanings - 'reckon' means to calculate, 'ornamental clasp' is a physical object, and 'approval' is the opposite of wistful's connotation.