ICY — the three-letter route
The first word is ICY. It fits the frozen hint and uses a compact three-cell corner of the board. Start at the I in row 4, column 2. Move left to the C in row 4, column 1, then move down to the Y in row 5, column 1. The letters read I → C → Y, with one turn between the leftward and downward moves.
For a precise check, the transcript is: 1 at row 4, column 2; 2 at row 4, column 1; 3 at row 5, column 1. This route spans two rows and two columns, visits two edge cells, and ends at a cell with one open orthogonal neighbor. It assigns three cells, leaving 16 open cells for the remaining words. If you were looking for a light hint, the row-5 Y is a natural place to test because its available continuation is limited.