The root word I'm thinking of is comfort; two types of prefixes are applied to it, in the words discomfort and uncomfortable. Why is this?
Depending on the context you want to use the root word, you will have to use a different prefix to explain what you mean.
Here the definitions of both words:
dis·com·fort (ds-kmfrt) noun
- Mental or bodily distress.
- Something that disturbs one's comfort; an annoyance.
un·com·fort·a·ble (n-kmfr-t-bl, -kmft-) adj.
- Ill at ease; uneasy.
- Causing anxiety; disquieting.
Even though both words use same root word and have a very similar meaning they are not synonyms, thus you would use each in a different context.
discomfort in a sentence:
Applying hot packs or hot moist towels may help relieve discomfort.
uncomfortable in a sentence:
Most patients consider the test to be only slightly uncomfortable.
There are a lot of similar prefixes (and suffixes, and roots). Some of the redundancy is because it comes from different languages. (For example, what is the difference between sept- and hept-? Sept- is from Latin, and hept- is from Greek.)
On the other hand, sometimes the same spelling means different things because it comes from both languages. (For instance, acr- in Greek means 'high' like in acrobat, whereas in Latin it means 'sharp' or 'bitter' like in acrimony.)
There are also some subtle differences in the meaning of the words in the original language. (For instance ab- and de- are both Latin, meaning 'away'. However, ab- was used as an ablative noun and de- was a preposition. You couldn't use them the same way, even if they had a lot in common.)