Unmarried, single, celibate, virgin, maiden are comparable as adjectives when they mean not united in bonds of marriage.
Unmarried merely states the fact; it is usually applied to those who have not yet married, but in law, it is applicable to a person who has been divorced and has not remarried and, sometimes, to one who has been widowed.
Single is applied to those who are not yet married but is commonly used of those who remain unmarried through life.
Celibate may be applied to the state of one having no expectation of marrying and it is especially applicable to that of one who is bound by a solemn vow to abstain from taking a mate. It is used chiefly of priests, monks, and nuns, of others who have dedicated their lives to religion, or of men or women who have accepted a way of life incompatible with having a spouse or children.
Virgin tends to stress a pure unsullied state of chastity. It usually applies to the unmarried but it may also be referred to the married when the marital relation has not been consummated, usually on grounds of choice.
Maiden holds much the same implications as virgin , but it often differs in its heightened implication of not having married and in its subdued suggestion of purity and freedom from sexual intercourse.