This is the 6419th most frequent Japanese word.
スイスイ
Smoothly; effortlessly.
スイスイ signifies smooth and effortless movement, often used to describe activities like swimming.
彼は泳ぎが得意なので、スイスイと泳いでいます。
Since he is good at swimming, he swims smoothly and effortlessly.
スイスイ implies an unblocked and efficient flow again, but this time applied to vehicles.
交通渋滞がなく、車がスイスイと進んでいます。
Without traffic congestion, the car is moving smoothly and unhindered.
スイスイ refers to ease and unobstructed progression, applied metaphorically to intellectual tasks.