Gottsui is a traditional Osaka word meaning “very”. The adjective is often used to describe something of an extreme nature.
Regarding the pronunciation of the word, there should be a short pause before the “t” (which is the purpose of doubling the letter when written in English):
go (short pause) tsui
You can toss this colorful word in front of most nouns and adjectives:
gottsui ninki - very popular
gottsui ki - a giant tree
gottsui ehh na - that’s really good
gottsuu - big/large (dropping the “i” and extending the “u” sound is is quite common in Kansai-ben)
Now go ahead and impress the locals with your Kansai Dialect!