Hematoma or Blood Blister: This is the most likely diagnosis due to the description of the bump being purple, which suggests bleeding under the skin. A hematoma or blood blister on the lip could result from trauma, such as biting the lip or a minor injury.

Angiokeratoma: A small, dark, vascular lesion that can appear on the lips. While less common, it could present as a purple bump.
Melanotic Macule: A benign pigmented lesion that can appear as a dark spot or bump on the lip, though it's typically flat.
Vascular Malformation: Abnormal formations of blood vessels that can present as purple lesions due to the concentration of blood vessels.

Kaposi's Sarcoma: A type of cancer that can cause purple lesions on the skin and mucous membranes, including the lips. It's particularly important to consider in immunocompromised patients.
Malignant Melanoma: Although rare on the lip, any new or changing pigmented lesion should be evaluated for the possibility of melanoma due to its potential severity.
Basal Cell Carcinoma or Squamous Cell Carcinoma: These skin cancers can occasionally present with pigmentation and should not be missed, especially in sun-exposed areas like the lip.

Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues, which can rarely cause purple lesions on the skin, including the lips.
Fabry Disease: A genetic disorder that can lead to the accumulation of a particular type of fat in the body's cells, affecting many parts of the body and sometimes causing skin lesions, including angiokeratomas that might appear on the lips.
Mucosal Lymphangioma: A rare benign growth of lymphatic vessels that could potentially appear as a purple bump on the lip, though it's more commonly associated with the tongue or other mucosal surfaces.