expression, adverb
straight from one place to another; while one is at it; on the way
Indicates doing something immediately after arriving or while still in the same trip, without returning home or making a separate trip. Often used with movement verbs like 行く, 寄る, 買う.
駅に着いたら、その足で会社に向かった。
When I arrived at the station, I went straight to the office.
買い物のついでに、その足で銀行にも寄った。
While I was out shopping, I also stopped by the bank on the way.
ついでに means 'while you're at it' and focuses on taking advantage of an opportunity, while その足で emphasizes the physical continuity of movement without a separate trip.
Literally 'with those feet', from その (that) + 足 (feet) + で (with). The phrase metaphorically extends the idea of using the same pair of feet to continue moving without interruption.