The prefix -de is of Latin origin. It's used before verbs and often has the meaning of negation or descent. Here's a short list of words with the prefix -de:
In the words decrease and deflate the opposite meaning is expressed with increase and inflate. In the case of descend, the opposite is ascend. The roots crease, flate and scend are bound morphemes because they never occur in isolation.
Many verbs can be combined with the prefix -de. The prefix corresponds to other English prefixes such as -in and -un which derive the opposite meaning. It only occurs in loanwords from Latin.