digraph ou

/aʊ/: cow, now, sour, vowel, towel,  plow, bough, plough
/u/:   coup, soup, through, slough, souffle
/o/:   though, borough, thorough, dough, trough (by bakers, cf below), furlough
/ɔ/:   cough, trough (in some lects)
 /ɑ/: cough, trough
/ʌ/:  rough, tough, hiccough (hiccup), chough, Clough, enough, scourge
/ə/:  Middlesbrough, UK; Doug



/ɔ/ > /o/ > /u/ > /aʊ/ (GVS)