How many syllables in acid?

Definition of acid:

acid (noun):

a sour substance

any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt.

any of various typically water-soluble and sour compounds that in solution are capable of reacting with a base (see base entry 1 sense 6a) to form a salt, redden litmus, and have a ph less than 7, that are hydrogen-containing molecules or ions able to give up a proton to a base, or that are substances able to accept an unshared pair of electrons from a base