The female equivalent to a male hard on. The woman's vagina swells up until it resembles a tazered, twitching piece of liver, and the man can enjoy a snug, responsive ride, much like a European Sports car that looks like the organ of a cow.
In due time, she had achieved a wide on. Fortunately Bert was finished before his ass cheeks collapsed.
A female equivalent to a hard-on. When experiencing intense erotic excitement, a lady's vaginal cavity expands to allow entry of penis/fist/vegetable etc. This causes a 'gap' that needs to be filled: a wide on. It is arguable that gay men can also experience an 'anal wide-on', which of course suggests that certain women could experience a 'double wide-on'.
Ooh that Brad Pitt's a real dish. He really gives me a WIDE ON!