Longman Dictionary of Contemporary English
n. 1 A bath in which an additive is poured directly into the water that creates bubbles. 2 A soap-based product to be added to a bath to create bubbles. 3 (context Cockney rhyming slang English) A laugh.
n. a bath in which you add something to foam and scent the bath water
A bubble bath is a filled bathtub with a layer of surfactant foam on the surface of the water and consequently also the surfactant product used to produce the foam. Less commonly, aerated or carbonated baths are called bubble baths.
Bubbles on top of the water, less ambiguously known as a foam bath (see photo), can be obtained by adding a product containing foaming surfactants to water and temporarily aerating it by agitation (often merely by the fall of water filling the tub). The practise is popular for personal bathing because of the belief that it cleanses the skin [http://avonshop.co.uk/product/bath-and-bodycare/bath/strawberry-sorbet-bubble-bath-1-litre.html?newdept=&s=tradedoubler&c=affiliates&otc=tradedoublerproductfeed_StrawberrySorbetBubbleBath1litre&bnd=&], that the foam insulates the bath water, keeping it warm for longer, and (as a lime soap dispersant) prevents or reduces deposits on the bath tub at and below the water level (called "bathtub ring" and soap scum, respectively) produced by soap and hard water. It can hide the body of the bather, preserving modesty or, in theatre and film, giving the appearance that a performer who is actually clothed is bathing normally. Children find foam baths particularly amusing, so they are an inducement to get them into the bathtub.
Surfactant preparations for this purpose are themselves called "bath foam", "foaming bath", or "bubble bath", and frequently contain ingredients for additional purposes common to bath enhancers. Used at much higher concentration (for instance on a washcloth), such preparations (especially in liquid format) may also be used to wash skin or hair, so they are sometimes marketed for combined purposes; in a few cases, mild household detergents for hand washing of articles have also been labeled for such purposes, or for preventing soap scum on the bathtub (with or without foaming).
Usage examples of "bubble bath".
He could tell at once that they carried different sorts of bubble bath mixed with the water, though it wasn't bubble bath as Harry had ever experienced it.
In her fantasy, she was devouring a mystery novel and chocolate chip cookies while she soaked in a hot bubble bath to ease the bruises that still ached a bit three days after her nasty adventure in the East End alley.
The package of bubble bath Deborah had tucked in the case had been irresistible.
I put Epsom salts in the water along with the bubble bath just in case.
There was a bathroom with a shower, and a bath and a loo, and free soap and bubble bath, and a bathcap, and three white towels.
She'd seen a news report on the television while lounging in a bubble bath and had found his cache of cash in his traveling case.
I was enjoying a bubble bath with Julie in a luxury suite in the Watergate Hotel.
She went and searched for the bubble bath, finally found the bottle in the trashcan—.