Dictionary.net

• Capable of uniting with five molecules of a monacid base; having five acid hydrogen atoms capable of substitution by a basic radical; - said of certain acids.

2010 - New Age Dictionary Database
By Oddity Software

• Capable of uniting with five molecules of a monacid base; having five acid hydrogen atoms capable of substitution by a basic radical; - said of certain acids.

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.