There are several dictionary programs for Palm devices. However only a few are able to use a custom-made dictionary. One which I discovered some years ago is KDIC, primarily designed for Japanese-English and similar. KDIC is not free, but will work perfectly while it is yet unregistered, displaying a small message under the definition.
KDIC website http://www002.upp.so-net.ne.jp/kei-k/
I have created a dictionary of use to Scrabble players. It is far from perfect, but it is at least somewhat useful.
Scrabble dictionary http://members.dodo.com.au/~sparrowfart/