In the word chimaek, maek comes from maekju, meaning beer. Chimaek is a Korean compound formed from chi-, referring to chicken, and maek-, a shortened form of maekju.
In Korean, beer is written 맥주 and romanized maekju. The first syllable, maek, is the part retained in chimaek, while ju is omitted to make the compact portmanteau used for the chicken-and-beer pairing.
Maekju is not the Korean word for soju, rice, or sauce. Soju is a separate distilled spirit, while makgeolli is a traditional milky rice wine. Those drinks may accompany Korean food, but they do not supply the “maek” in chimaek.
The beer connection also explains why chimaek is more than a general fried-chicken dish. It specifically names the social combination of fried chicken and beer, especially popular in restaurants, at festivals, and during televised sports.