There are many words that can be used as synonyms for the phrase "hobby horse." Some of these include: 1. pastime 2. interest 3. obsession 4. amusement 5. diversion 6. recreation 7. pursuit 8. avocation 9. fancy 10. preoccupation Each synonym carries a slightly different connotation. "Pursuit," for example, suggests a pursuit of excellence, while "preoccupation" implies a hobby that is consuming. "Avocation," on the other hand, suggests a leisure activity that is enjoyed as an intellectual or artistic pursuit. Overall, the use of synonyms for "hobby horse" helps to add richness and nuance to our language, allowing us to more precisely express our thoughts and feelings about our favorite pastimes.