Wash. Rev. Code § 73.16.900
For the purposes of this chapter, the terms spouse, marriage, marital, husband, wife, widow, widower, next of kin, and family shall be interpreted as applying equally to state registered domestic partnerships or individuals in state registered domestic partnerships as well as to marital relationships and married persons, and references to dissolution of marriage shall apply equally to state registered domestic partnerships that have been terminated, dissolved, or invalidated, to the extent that such interpretation does not conflict with federal law. Where necessary to implement chapter 521, Laws of 2009, gender-specific terms such as husband and wife used in any statute, rule, or other law shall be construed to be gender neutral, and applicable to individuals in state registered domestic partnerships.
RCW 73.16.900