Identify Black Spider
This spider appears to be a velvety black---rather than a slick and shiny black. Also the legs are roughly equal in length rather than fore and aft longer than the two in the middle. Finally, the abdomen is much longer than wide----definitely not bulbous.
This is a female house spider---Family Filistatidae, genus Kukulcania sp. These can be fairly common in homes, especially under heavy furniture with short legs. The females can make some tough, almost sheet-like webbing under things like rockers, sofas, dish hutches, etc., etc. These are most likely to be found---or their webs---when heavy furniture is being moved or turned on its side or turned over for repair. Male Kukulcania are smaller, thinner and various brown tones more or less swirled together.
These spiders may be large enough to bite but the venom is not known to be harmful to humans or pets.
Spraying for spiders might sound appealing, but it doesn't do much to the existing spider populations in a home. You will find that you have to almost literally drown the critter in insecticide to slow it down and eventually kill it. That approach doesn't work at all when the spiders have created their webs up and under the short legs of some piece of furniture.
If they are especially bothersome, find a stiff broom that can be shoved under heavy furniture periodically---twist and sweep it around under the furniture and pull it out again. Disturbance is one 'enemy' of these spiders and squashing or hurting them with the broom is another. For any spider out in the open, like this one was, a handy yogurt or cottage cheese container and a piece of stiff paper or light cardstock can be used to trap and remove the critter to the outdoors.
When all else fails, smack them with a rolled up paper, magazine or fly swatter.
So, no---this is NOT a widow of any kind and there's no risk to people, pets or wildlife.
As for who or what was a Kukulcania? Kulculcan was one of 3 great culture heroes of the Mayan Indians. The name means 'plumed serpent'. Kukulcan is equivalent to the Aztec god Quetzalcoatl.. Both of these magical individuals were supposed to have come from afar, brought cultural and technical benefits (including writing), disappeared, and were expected to return in time. Kukulcan was represented with protruding teeth, a pendulous nose and a lolling tongue. This makes the spider sound so much prettier?
I hope this helps........