I use the Janes Aerospace Dictionary (I have an old copy, followed me from uni into industry). Very comprehensive and in my opinion the best dictionary around.
Now it been superceeded by Cambridge Aerospace Dictionary (750 pages)
http://www.cambridge.org/uk/catalogu...sbn=0521841402
If you want the latest acronym being used (and aviation loves creating new acronyms), buy the latest Cambridge Dictionary, otherwise a second hand Janes Dictionary will be ok for technical definations (look on the web for some for sale)