All 16 words, sorted alphabetically. Group them into four categories of four.
The four category names, easiest to hardest. No words revealed yet.
Theme name plus one word from each category.
BUNKER (golf sand trap), DESERT (sandy landscape), HOURGLASS (sand flows through it), and SANDBOX (filled with sand for play) are all places where sand is found.
METRONOME, PENDULUM, SWING, and WINDSHIELD WIPER all move back and forth in a repeated oscillating motion.
BARRE (ballet-inspired bar class), REFORMER (Pilates machine class), SPIN (stationary bike class), and STEP (step platform class) are all exercise classes named after their apparatus.
CUCKOO CLOCK (cuckoo bird pops out), FROOT LOOPS (Toucan Sam is the mascot), MEXICAN FLAG (eagle eating a serpent), and WEATHER VANE (often shaped like a rooster) all feature birds.