lama

One root, and the figurative sense is standard. The Reta Vortaro gives lama two readings and both are ordinary: unable to walk properly, and, of an argument or an excuse, unconvincing. English does exactly the same thing with a lame excuse, so the second sense costs an English speaker nothing to learn. The verb is lami, to limp, and it too has the figurative reading: a plan that lamas is one that does not quite work.

The homograph to know about. Lamo with an -o is not lameness. It is the llama, Lama glama, the South American animal, and the two words are unrelated roots that collided. Lameness is lameco, and a lame person is lamulo. So lama and lamo are not the adjective and noun of one root, however much they look it.