Some words ending with the letters "gh" pronounced as "f" are: rough, tough, enough, cough, laugh.
Some words ending in GH are:boughcoughdoughenoughhighlaughneighnighroughsighsleighthighthoroughthroughtoughugh
ghost
ghag
Words with 'gh' and 'kn' sounds are known as consonant clusters. The combination of 'gh' produces sounds like /f/ in words like "enough" or /g/ in words like "ghost." The 'kn' cluster typically produces the /n/ sound in words like "knight" or "knit."
brightlycougheddelightfuldoughtyfightingfrightenedhighlighthighlyhighpointhighwayinsightfullaughinglightningmightilynaughtyneighborsnightfallnightgownnightmarenighttimerightfullysleighedslightlystraightenthoroughlytoughness
laugh
toughen throughout heighten lighten
there are many through rough though
ghat, ghee, ghis
ugh.
The "gh" in "laugh" comes from Middle English influence, where the "gh" was used to represent the "f" sound. Over time, English spelling has evolved to reflect the historical roots of words, even if the pronunciation changes.
Although "gh" has the sound of "f" in some words with "ough" (and "laugh"), the words though, high, and night have a silent gh, the words ghost and aghast have a silent h, and the word bigheartedseparates the pair into two syllables.