Faecal means ‘of faeces’: about the solid waste that comes from the bowel. It is a hospital-and-laboratory word. You will see faecal matter, faecal bacteria, faecal samples — talk about dirt in water, disease, or tests. Nobody says it at the table; it wears a white coat. This is the British spelling. American English writes fecal, one letter simpler, same meaning, same sound (FEE-kuhl). If a sign says a beach is closed because of faecal contamination, it means waste has got into the water, and that is a health warning, not a rude joke.