Is headache a countable noun? How about toothache? And stomachache? – Limuzi, China
A count noun (or "countable noun") is a noun that can be counted, can be plural, and can be used with both singular and plural nouns. Headache, toothache, and stomachache are all count nouns because they meet those three criteria, as shown in the examples below.
These “ache words” are more commonly used in their singular form, probably because people have only one ache at a time, but what matters is that these words do have a plural form and can be used with a plural verb.