There are different systems of romanization of hangeul. The official romanization in South Korea, today probably the most common and in my opinion also the easiest to use, is the Revised Romanization. Unlike the McCune–Reischauer system there are no breves and apostrophes used.
옆 차기 yeop chagi
eo since it's ã…•, a shorter and different o-sound than the ã…— in Taekwondo or dobok.
Yeop chagi would be the up to date Kukkiwon term.
I think General Choi's called the side-kick 'thrusting side kick' in the first edition of his Taekwon-Do textbook from 1965. Don't have it with me right now, so I can't double check.
옆차 지르기 yeopcha jirugi
So while 지르기 is translated as 'punch' most the time we have to realize that there sometimes isn't just one meaning for a Korean word.
General Choi's Taekwon-Do still has a huge influence on TKD in the US and some parts of Europe and that's why certain names for techniques may still be used.