Nglish is a Germanic language. What does this mean, and how true is it?

Charles Barber, The English Language: A Historical Introduction (Cambridge Approaches to Linguistics), Cambridge: Cambridge University Press, 1992
[Cheap, comprehensive and clear, but quite demanding]
Albert C. Baugh and Thomas Cable, A History of the English Language, 5th edition, London: Routledge, 2002
[Good on vocabulary, with useful index; earlier editions are often available second hand and are just as useful; does not ask too much of the reader]
Barbara Fennell, A History of English: A Sociolinguistic Approach, Oxford: Blackwell, 2001.
[Good on history and society: accessible on language]