According to the Washington State University Extension, the only venomous spider in Washington that is dangerous to humans is the western black widow (Latrodectus hesperus). Mostly, these spiders are found in Eastern Washington, with just a few showing up in Western Washington.
Spiders are arachnids with fangs that inject venom when they bite. Therefore, "venomous" is the proper term in relation to spiders, and some are more dangerous than others.
Even though a spider may not be venomous, some people can have an allergic reaction to even non-venomous spider bites.
The most common spider in Western Washington is the "hobo spider" (Tegenaria agrestis), also called the aggressive house spider. This spider can cause a severe reaction in someone who is allergic to spider venom.
If you are bitten by a spider and can trap it, take it to the County Extension Office for identification.
If you are bitten by a spider and it causes more than a mild irritation, seek medical advice.