A person, such as a family member or close friend, who is important or influential in one's life: “The most important variable in successful smoking cessation is the support of significant others in the new nonsmoker's life” (Carolyn Reuben)
If you refer to your significant other, you are referring to your wife, husband, or the person you are having a relationship with. your husband, wife, girlfriend, or boyfriend
Any person with whom a child or adult has a relatively long-lasting emotional tie, who is uniquely important to the individual, and who is interchangeable with no one else (See also attachment figure)
An important individual who plays a major role in the life of a subject in addition to the subject's spouse or close relatives or in lieu of a spouse or close relative