bind <key> backward_word

Move the cursor left to the beginning of the current or previous word. If the cursor is not on the first character of a word, it is moved left to the first character of the current word. If the cursor is on the first character of a word, or on a space, or at the end of the input line, it is moved left to the first character of the previous word. If the cursor is at the start of the input line, it does not move.

If the new cursor position is close enough to the left edge of the screen, the input line might be shifted to the left and redrawn.