from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Symbol for the picohenry, an SI unit of electrical inductance equal to 10−12 henrys.
- abbr. The negative of the logarithm to the base 10 of the concentration of hydrogen ions, measured in moles per liter; a measure of acidity or alkalinity of a substance, which takes numerical values from 0 (maximum acidity) through 7 (neutral) to 14 (maximum alkalinity).
p(otential of) h(ydrogen).(American Heritage® Dictionary of the English Language, Fourth Edition)
From p, denoting negative logarithm, and H, denoting hydrogen. (Wiktionary)