prowess » poweress
Spotted in the wild:
- The whole point of the Warez sub-culture is to get the pirate program released and distributed before any other group. I know, I know. But don’t ask, and it won’t hurt as much. This is how they prove their poweress. (Ozone Pilot, quoted in the Jargon File, s.v. warez d00dz)
- To show his poweress, Keenan proudly describes the details of his rape of Dr. Nathan. (HBO.com - profile of a character in the series Oz)
The word prowess is now quite opaque, the relevant sense of prow (an etymological doublet of proud) being long since obsolete. The semantic, orthographic, and phonological similarity between prowess and power makes poweress a very natural reanalysis.
(Searching for instances of this eggcorn is made slightly more difficult by the existence of something called PowerESS, in which the ESS stands for “Employee Self-Service.” On Google, limiting the search to English pages helps a great deal.)