Oral - aural
One reason for the confusion between oral and aural is that they are very similar in pronunciation, IPA: /'ɔː rəl/. They are used in very similar contexts. Both are to do with spoken language. Their meanings, however, are in a sense opposite. Oral is to do with the mouth, and so speaking - it comes from the Latin word ōs (genitive ōris) meaning 'mouth'; and aural is to do with the ears, and therefore listening - it comes from the Latin auris meaning 'ear'.
According to the OED, the first syllable of aural is a pure vowel like that of 'awe'; whereas the first syllable of oral is more of a diphthong, like 'oh', IPA: /əʊ/. This is a very slight distinction. In many mouths, the two words are normally indistinguishable.
Many modern speakers prefer to pronounce aural as it looks, with the first vowel sounded like that in 'how', IPA: /'aʊ rəl/. This has the merit of being less ambiguous, though some academics sneer at it on the grounds that it is changing the way English is traditionally spoken. If you are teaching or lecturing and want to make the distinction clear to your audience, it is sensible to exaggerate the pronunciations.
- You may also want to see AWE's article on a nicety of usage at Oral - verbal.