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.
ADHERE, AFFIX, GLUE, and STICK all mean to fasten or attach something using an adhesive or bonding method.
COMMERCE, CONGRESS, INTIMACY, and RELATIONS are all polite or euphemistic terms used to refer to sexual activity.
FOUL, SPARE, SPLIT, and STRIKE are all terms used to describe specific outcomes or situations in the game of bowling.
CLEAVE (split apart / cling together), GARNISH (add decoration / seize wages), OVERSIGHT (careful supervision / a mistake of inattention), and SANCTION (to permit / to penalize) are all contronyms — words with contradictory meanings.