Take a random number between 0 and 75 and use it as the argument for the head command to select that number of lines from the file /usr/share/dict/words. Then take another random number between 0 and 75 and use it as the argument for the tail command to select that number of lines from the output of the head command.
head -n $(shuf -i 0-75 -n 1) /usr/share/dict/words | tail -n $(shuf -i 0-75 -n 1)