Longest key on a keyboard

SPACEBAR

["Think about the key that you use most frequently while typing to separate words."]

The clue "Longest key on a keyboard" leads to the answer "SPACEBAR" through a straightforward and literal interpretation. The clue is asking for the key on a standard keyboard that is physically the longest. On most keyboards, the spacebar, which is used to insert spaces between words, is the longest key, stretching across the bottom center of the keyboard. Therefore, the answer to the clue is "SPACEBAR."