그동안
geudongan · TOPIK 1
during that time, meanwhile
⏳ 그 (that) + 동안 (span of time) = during that time
그 is the demonstrative that, and 동안 means a period or duration. Joined, they literally say that period, which is why 그동안 covers both meanwhile and all this while, as in 그동안 잘 지냈어요? (Have you been well all this time?).