I had to check a few sources on this one, but the prefix is "ex-." Tend means, "Regularly or frequently behave in a particular way or have a certain characteristic. The prefix "ex-" means "out, away from, outside." So outside of what tends to be normal.
dam is the symbol for decametres. A decametre is 10 metres. Decametres are not regularly used, the prefix is an historical anomaly.
when it isnt at the end of a word
Yes, prefix does have a prefix. The prefix is pur-.
"pre- " is the prefix of prefix
The word itself is not an prefix However, it does have a prefix The prefix is -less.
Demi has no prefix; it IS a prefix.
The prefix is in. The prefix in- means not.
The prefix is micro.
The prefix is in-. This prefix means not.