False Widow

A woman who falsely claims widowhood. Usually to avoid the stigma of having a child with no husband, or to escape a loveless marriage, or to play on people's pity for widows. Can be depicted as a Wicked Widow or a Wonderful Widow, depending on the circumstances.

Examples of False Widow include:

Comic Books

In a bizarre twist on this trope, Victor Mancha of the Runaways comic books thinks that his dad was a marine who died in the first Gulf War. It turns out that he never had a dad in the traditional sense at all--Victor is a cyborg created by the evil robot Ultron using his mother's DNA.

Wavey Prowse in The Shipping News (book by Annie Proulx) and (2001 film). She claims that her disabled son's father was lost at sea, but ultimately reveals that, after a long string of affairs, he'd left her when she was eight months pregnant and is now living somewhere outside Newfoundland. Instead of admitting what happened, she'd staged his supposedly-fatal shipwreck to save face.
Inverted in Bounce: Gwyneth Paltrow's character is a widow but claims to be divorced because she was sick of people pitying her. Since, in her words, "everyone is divorced these days", they don't pity her as much when she tells that lie.

Fawn at the beginning of The Sharing Knife by Lois McMaster Bujold claims to be a "grass widow" to explain why she is pregnant and alone. Dag delicately inquires if she knows what a grass widow is. Fawn had thought it meant a woman recently widowed; it really meant a woman in her exact situation, never married but claiming to be widowed in order to escape the stigma of unwed pregnancy.

It seemed she'd told the truth despite herself.

One of the earliest examples is Helen Graham from Anne Bronte's The Tenant of Wildfell Hall. She's escaping a horrible marriage.
Maxi in the novel I'll Take Manhattan decides that it's much cooler to be a widow than a teenage divorcee, and fakes being a widow (runs around in black, sighing tragically, what have you) instead. In her defense, she was 19 and way dumb for it.
The topic was discussed in one of the Anne of Green Gables books. In one of those "out of the mouths of babes" situations, a schoolgirl expresses the desire to be a widow. Consider that this is the nineteenth century, where divorce is practically unknown and being unmarried is socially unacceptable. A widow gets the best of both worlds.
Vianne in The Lollipop Shoes (a.k.a. The Girl with No Shadow) changes her name and pretends to be a widow to explain the existence of her two children.
Pharinet in Chronicles of Magravandias claims widowhood even though there's no solid proof her husband is dead. It serves the practical purpose of letting her move out of her husband's house and back with her own family, which she always wanted.
In The Grimnoir Chronicles short story Detroit Christmas, Emily Fordyce hires Sullivan to prove her missing husband is dead. This whole thing is actually an elaborate plot by her to fake his murder and run away with the insurance payout+inheritance before he returns from a vacation with his mistress.

A male version in an episode of CSI: Miami had the Villains of the week being a group of con artists posing as a widower and his two children (actually a 30 something married couple) murdering a man in order to use his wife as a means to get into a yacht club and steal gold from another of its members.
In an episode of Carnivale, Sophie pretends to be a widow in order to get into bed with a random stranger in town.
Constance MacKenzie in Peyton Place. She moves away from her small town and has an affair with a married man, who dies shortly after impregnating her with their illegitimate daughter, Allison. Forced by the circumstances to return to said small town, Constance takes the dead lover's name and pretends to be his widow, even altering Allison's birth certificate by one year to make her appear legitimate. Allison has a Heroic BSOD after learning the truth (and finding the corpse of her best friend's mother hanging in her bedroom closet).