Swollen lump on thigh half the size of my palm. unsure how long it's been there. looks like a contusion or swelling but no bruising? tumor?

Concerning...: Are you having any other symptoms such as fevers, unexplained weight loss, new onset fatigue? Any lumps anywhere else on your body? Is the lump tender to the touch? Something that large, in that location that does not look like a bruise, and you don't remember injuring that area would make me want to get it examined by a doctor sooner than later. May be nothing, but hard to tell from here.

Concern: One must be concerned about a hematoma if you have sustained an injury to the area. If you have not, then one must be suspicious of a tumor, either benign (for example a lipoma or fatty tumor) or malignant (a sarcoma). This is worth getting checked out!