do you mean Reduction of vowels or reduction of words into shorter words?
reduction of vowels would be like when a vowel becomes unstressed when a word changes.
eg., endoscope -> endoscopy.
[ˈɛndəskəʊp] -> ɛnˈdɒskəpi
notice how the əʊ becomes ə when the scope syllable becomes unstressed?
another example would be with 'the'. when unstressed, the vowel gets reduced.
the ðɪ: -> ðə
an elision is when a sound is removed from a word in running speech.
eg., probably -> pronounced 'probly' = b elided
should have (should ov) -> shoulda = f (v) elided
you can see how that differs from the phonological sense of reduction - with reduction the sound is still there, but changed, with elision the sound is missing.
i guess a reduction with respect to words is when you have phone for telephone, tele for television, doc for doctor, prof for professor etc.