Hello, Is this lump in a location where you would have a wisdom tooth? A possibility could be a tooth starting to erupt or one tipped and not able to continue erupting. You may feel the soft tissue over the hard tooth structure. If your wisdom tooth was already extracted, you may have some residual tissue that appears as a lump. A cyst can feel like a harder lump under the gum. The size description would make this a consideration. Look for any changes especially a rapid increase in size. An abcess or pocket of infection could be present and require dental treatment. A growth could be a tumor and should be further evaluated. Lumps that appear hard with thin tissue covering can be excess bone called tori or an exostosis. These do not tend to be sensitive, but often are noticed once damaged. How did you notice this area? Was there any trauma? More information would allow me to provide more suggestions. Anti-inflammatory medications can assist in reducing swelling and assist healing in many circumstances, but not necessarily with your description. Warm salt water rinses offer a cleansing effect. Keep up good daily oral care. Proper nutrition with balanced vitamins is recommended. Thank you for your inquiry. I would be glad to include additional suggestions with more details. A visit to your dentist with a clinical exam would provide the best diagnosis and relieve your concern over a serious condition.