I have a tattered Oxford dictionary, a Webster which I don’t like to use, two thick tomes of World Book dictionary and two Roget’s thesaurus. Nowadays I hardly refer to these writing tools. I find the online dictionary and thesaurus so much more easy to use. All I have to do is to key in the word and the explanation pops up in a jiffy. No more leafing through pages and squinting at small print.
Dictionary.com and Thesaurus.com are very useful but if I’m looking for some grammar references in addition to word definition, Encarta is where I go to. For example, this morning I was searching the word ‘series’ as I wasn’t sure what the singular form of the word is. I found this useful explanation on the Word Usage box at the bottom of the page.
Series can be a singular or a plural noun, depending on its meaning. When it is used to refer to a single set of things, it takes a singular verb even if it is followed by the preposition of and a plural noun: A series of medical tests is planned for next week. When series refers to two or more sets of things, it takes a plural verb: Three series of medical tests are planned for next week.

Thank you, exactly what I was looking for. I am a non-native English teacher and wasn´t sure whether I was right when I said it can be used in both singular and plural
Nina
continua
thank you,for this.I can reply my teacher already.
Garn from Thailand.
Thank you for simplifying this concept. You made it ‘crystal clear’.