It’s pronounced to rhyme with “good” in Northern England, but then so are words like “mud” and “bud” as well. The distinction between /ʌ/ (as in “blood”, “luck”, “putt”, “bugger”) and /ʊ/ (as in “good”, “look”, “put”, “booger”) is called the foot-strut split. It developed in Southern England and was exported across most of the rest of the English speaking world without a consistent spelling between the two vowels having developed.

English used to have two vowels, /u:/ (as in “food”, “moon”, “loose”) and /ʊ/, which were usually respectively spelled and , but /ʌ/ did not yet exist. At some point, people began to develop two different pronunciations of what used to be /ʊ/ - if the preceding consonant involved the lips and the following consonant involved the front of the tongue, it stayed /ʊ/, as in “put”, “pudding”, “wool” (which used to be spelled “wull”). Elsewhere, it shifted from /ʊ/ to /ʌ/, as in “luck”, “pup”, and “hull”. Both before and after this split occurred, some words which had /u:/ were prone to irregularly shifting to have /ʊ/ instead, including words like “look” and “foot” (ironically meaning that the foot-strut split is a misnomer since “foot” had /u:/ when /ʊ/ was undergoing the split). For those /u:/ words that shifted early enough, like “blood” and “flood”, they were actually eligible to undergo the foot-strut split, and ended up on the /ʌ/ side of things despite the spelling.

Variation between /u:/ and /ʊ/ continues to this day. In some dialects without the foot-strut split (and thus no /ʌ/), words like “foot” and “look” can still have /u:/. In dialects with the foot-strut split, some words like “room”, “broom”, “roof”, “root”, and “soot” can have either /u:/ or /ʊ/.