-ough words -- First Group
The first group shows two different developments from a long [u] sound:
|Middle English sound||ME spelling||ModE spelling||MnE sound|
[x] is the voiceless velar fricative as in Scots dialect loch.
The top examples show the loss of the final fricative, and the long vowel becomes a diphthong through the the Great Vowel Shift. When the fricative was retained and changed to [f], the vowel was shortened.