School with American vowel sound? (5)
I believe the answer is:
schwa
'vowel sound?' is the definition.
(schwa is a kind of vowel sound)
'school with american' is the wordplay.
'school' becomes 'sch'.
'with' becomes 'w' (abbreviation).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'sch'+'w'+'a'='SCHWA'
(Other definitions for schwa that I've seen before include "Indistinct sound" , "Uh' sound" , "sound unstressed" , "Stress-free sound" , "Unstressed vowel (phonetics)" .)