Lipoma: A common, benign tumor composed of fat tissue. It is often painless, immobile, and can be found in various parts of the body, including the thigh. Lipomas are usually non-cystic and can grow to a considerable size.

Fibroma: A benign tumor of fibrous or connective tissue. It can present as a firm, painless lump and is generally immobile.
Hematoma: A collection of blood outside of blood vessels, which can occur due to trauma. Although it might initially be painful, an old hematoma can become painless and feel like a firm, immobile lump.
Scar tissue or keloid: Especially if there's a history of trauma or surgery, scar tissue can form a lump that is firm and non-tender.

Soft tissue sarcoma: Although rare, sarcomas are malignant tumors that originate from soft tissues like muscles, fat, and connective tissues. They can present as a painless lump and are critical to diagnose early due to their potential for aggressive behavior and metastasis.
Lymphoma: Certain types of lymphoma can manifest as a lump in the thigh, especially if there's involvement of lymph nodes in the area.

Neurofibroma: A benign nerve sheath tumor that can occur in the thigh. It's more commonly associated with neurofibromatosis type 1 but can occur sporadically.
Desmoid tumor (aggressive fibromatosis): A rare, benign but locally aggressive tumor that can occur in the thigh. It's known for its potential to cause significant morbidity due to local invasion.
Myositis ossificans: A condition where there's heterotopic ossification of soft tissues, often following trauma. It can present as a firm, painless lump in the muscle of the thigh.