grammar

Double-click on any word and see its definition from Cambridge Dictionaries Online.

"Is splitting of an infinitive considered bad English?"

http://www.wsu.edu/~brians/errors/nonerrors.html#split

"How do you change singular to plural?"

http://www.edufind.com/english/grammar/NOUNS2.cfm

"What are figures of speech?"

http://www.robibrad.demon.co.uk/Idioms.htm

"When do we use had better?"

http://www.better-english.com/grammarexplanations/hadbetter.htm

"What is the difference between slang and Cockney?"

According to the Cambridge Online Dictionary slang is:

informal language, which might include words and meanings which are not polite and which might stay in use only for a short time. It is used by particular groups of people who know each other, and is usually spoken rather than written:

Cockney is: (the way of speaking of) a person from East London, especially the poorer part:

and Cockney rhyming slang:

refers to slang which is used instead of a word or phrase and which rhymes with it.

In short, Cockney (rhyming slang) is just one type of slang.

"What's the difference between pray and prey?"

http://www.wsu.edu/~brians/errors/pray.html

"What's the meaning of concordance?"

The Cambridge Online Dictionary says:

concordance noun [C] SPECIALIZED

a book or list which is an alphabetical collection of the words used in a writer's work with information about where the words can be found and in which sentences.

concordance verb [T] SPECIALIZED