Sentence:  This buffer , <WSD>pH</WSD> 8.6 , was 0.005 M in * * f and 0.039 M in tris ( hydroxymethyl ) - aminomethane ( Tris ) . 
Meaning of the word marked with <WSD> tags:  (from potential of Hydrogen) the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution (where 7 is neutral and greater than 7 is more basic and less than 7 is more acidic);