Dictionaries relating to research methodology
Jupp, V. (ed.) (2006) The Sage Dictionary of Social Research Methods, London, Sage.
Miller, P. McC. and Wilson, M. J. (1983) A Dictionary of Social Science Methods, Chichester, John Wiley.
Miller, R. L. and Brewer, J. D. (eds.) (2003) The A-Z of Social Research, London, Sage.
Payne, G. and Payne, J. (2004) Key Concepts in Social Research, London, Sage.
For dictionaries of statistical terms:
Everitt, B. and Wykes, T. (1999) A Dictionary of Statistics for Psychologists, London, Hodder-Arnold.
Nelson, D. (2004) The Penguin Dictionary of Statistics, Harmondsworth, Penguin.
Upton, G. and Cook, I. (2006) A Dictionary of Statistics, Oxford, Oxford University Press
For a dictionary of terms specifically relating to qualitative research, see
Schwandt, T. (2007) The Sage Dictionary of Qualitative Inquiry, Thousand Oaks CA, Sage
Encyclopaedias
A relatively comprehensive and specialist encyclopaedia on social research methodology is:
Lewis-Beck, M., Bryman, A., and Liao, T. F. (eds.) (2004) The Sage Encyclopedia of Social Science Research Methods, Thousand Oaks CA, Sage. (Multiple volumes.)
Entries in this encyclopaedia vary in their level of technical difficulty.
General social science encyclopaedias:
Smelser, N. J. (ed.) (2001) International Encyclopedia of the Social and Behavioral Sciences, Amsterdam, Elsevier. (Multiple volumes.)
Sills, D. L. (ed.) (1968) International Encyclopedia of the Social Sciences, New York, Macmillan. (Multiple volumes.)
Ritzer, G. (ed.) (2006) The Blackwell Encyclopedia of Sociology, Oxford, Blackwell. (Multiple volumes.)
Dictionaries and Encyclopaedias of Philosophy
When I come across philosophical terms or issues about which I require more information; there is a large number of dictionaries and encyclopaedias most of them being reasonably accurate, though you will find they vary in their helpfulness, for example according to how much background knowledge they assume.
A useful general source on modern thought is the following:
Bullock, A., Stallybrass, O., and Trombley, S. (eds.) (2000) The New Fontana Dictionary of Modern Thought, London, Fontana
For a useful reference book on postmodernist thought:
Sim, S. (1998) The Icon Critical Dictionary of Postmodern Thought, Cambridge, Icon Books. (second edition published as The Routledge Companion to Postmodernism, London, Routledge, 2004.)
An alternative is: Taylor, V. E. and Winquist, C. E. (eds.) (2003) Encyclopedia of Postmodernism, London, Routledge.
Useful sources for philosophy:
S. Blackburn (2007) The Oxford Dictionary of Philosophy, Second edition, Oxford, Oxford University Press.
Mautner, T. (1999) The Penguin Dictionary of Philosophy, Harmondsworth, Penguin.
Other useful sources include:
Audi, R. (ed.) (1999) The Cambridge Dictionary of Philosophy, Cambridge, Cambridge University Press.
Craig, E. (ed.) (1998) The Routledge Encyclopaedia of Philosophy, London, Routledge.
(Multiple volumes. There is also a Concise or Shorter, single volume, version of this encyclopaedia.)
Edwards, P. (ed.) (1973) The Encyclopedia of Philosophy, New York, Macmillan.
(Multiple volumes.)
Honderich, T. (1995) The Oxford Companion to Philosophy, Oxford , Oxford University Press.
[Note that there are more than one edition of many of the above books, and you may find that older editions will suffice, many of which can be bought quite cheaply second hand. Later editions, or more recent books, are not necessarily superior.]
ONLINE SOURCES
There are not many online sources for clarification of methodological terms used in educational research, however, there are some relevant entries in the Online Dictionary of the Social Sciences, which can be found at: http://bitbucket.icaap.org/dict.pl (last accessed 19/03/15)
There are some reliable, and many less reliable, sources of information about philosophy on the internet. A reasonably reliable source is the Stanford Encyclopedia of Philosophy, which can be found at: http://plato.stanford.edu/ (last accessed 19/03/15) Also of value is the Internet Encyclopedia of Philosophy, which can be found at: http://www.iep.utm.edu/r/ (last accessed 19/03/15) The Meta-Encyclopedia of Philosophy compares the entries on the same topics across several online resources. This can be found at: http://www.ditext.com/encyc/frame.html (last accessed 19/03/15)