This is the gh /-/ and gh /f/ sounds
The gh letter combination can be silent or it can make an /f/ sound
Generally, when gh is in the middle of a word it is silent, when gh is at the end of a work it sounds like /f/
This is not always true, there are exceptions to this
Word Lists
gh /-/
bought
brought
caught
daughter
fought
naughty
slaughter
plough
thorough
though
although
thought
thoughtless
through
gh /f/
laughter
coughing
enough
roughly
tougher
troughs