Cortavidrios
I understand that the article must agree with the noun in number and gender but I have seen the word "cortavidrios" (glass cutter) used with "un" or "el." So is this word actually singular even though it ends in an "s". Thanks.
2 Answers
There are a number of essentially combination words that combine something with the plural form of a noun to make a new word that ends in s, in the singular.
Examples:
parabrisas
limpiaparabrisas
paraguas
These words tend to end in s, have a plural that is the same and only signaled by change in article (el parabrisas, los parabrisas), and tend to be masculine.
Cortavidrios is not in the RAE, but is in oxford:
http://lema.rae.es/drae/?val=cortavidrios
http://www.oxforddictionaries.com/us/translate/spanish-english/cortavidrios
When used with un or el, it would indicate you are only talking about one of them.
Gracias