What is the unstressed vowel in marvellous?

The unstressed vowel in "marvellous" is the schwa sound, which is represented by the symbol /ə/. In this Word, the schwa sound is found in the second syllable, "vel," where the 'e' is pronounced as /ə/. The schwa sound is a neutral, mid-central vowel sound that is very common in English pronunciation, especially in unstressed syllables.