"ough" can be pronounced in TEN DIFFERENT WAYS

Ough is a letter sequence often seen in words in the English language. In Middle English, where the spelling arose, it was probably pronounced with a back rounded vowel and a velar fricative, e.g., [oːx] or [uːx]. It is by far the sequence of letters with the most unpredictable pronunciation, having at least six pronunciations in North American English and over ten in British English. A few of the more common are these:

• /oʊ/ as in "though" (cf. toe).
• /uː/ as in "through" (cf. true).
• /ʌf/ as in "rough" (cf. ruffian).
• /ɒf/ as in "cough" (cf. coffin).
• /ɔː/ as in "thought" (cf. taut).
• /aʊ/ as in "bough" (cf. to bow).

Pronunciation	Example	Comment
/ʌf/	tough, enough, hough	Compare "huff"
/ɒf/	cough, trough	Trough is pronounced /trɒθ/ by some speakers of American English
/aʊ/	bough, plough	Pronounced like the word 'Ow'
/oʊ/	though, dough
/ɔː/	thought, bought	Regularly used before /t/, except in drought /draʊt/
/uː/	through, brougham
/ə/	thorough, borough	Both pronounced /oʊ/ in American English
/ʌp/	hiccough	Variant spelling of "hiccup", though the latter form is recommended in both British and US
/ɒk/	hough	More commonly spelled "hock" from the 20th Century onwards
/ɒx/	lough	A lake; Irish analogue of Scots "loch"

Note that "slough" has three pronunciations according to meaning:

• /sluː/ (as in, "slogging through a slough of mud")
• /slʌf/ (as in "to slough off")
• /slaʊ/ the town of Slough in Berkshire in England

Other pronunciations can be found in proper nouns, many of which are of Celtic origin (Irish, Scottish, or Welsh) rather than English.

• For example ough can represent /ɔːɡ/ in the surname Coughlin, /juː/ in Ayscough and even /iː/ in the name Colcolough (/koʊkliː/) in Virginia.

The original pronunciation in all cases except hiccough was the one of lough. However the /x/ sound has disappeared from most modern English dialects. As it faded, different speakers replaced it by different near equivalents in different words (namely, /f/, /w/ → /ʊ/, /ː/, or /k/).
The two "ough"s in the English place name Loughborough are pronounced differently, resulting in Luffburruh. Additionally, three parishes of Milton Keynes--Woughton /ˈwʌftən/, Loughton /ˈlaʊtən/ and Broughton /ˈbrɔːtən/--all have different pronunciations of the combination.

• Tough, though, through, and thorough are formed by adding an additional letter each time, yet none of them rhymes with another.

A comparable group is omb, which can be pronounced in at least four ways: bomb /bɒm/ (rhymes with Tom), comb /koʊm/ (rhymes with home), sombre, and tomb /tuːm/ (rhymes with gloom).
augh is visually rather similar to ough but admits much less pronunciation variation.

• /æf/, /ɑːf/ as in "laughter"
• /ɔː/ as in "daughter"

Source: Wikipedia, the free encyclopedia