The term "certain months of the year" can be substituted with various synonyms depending on the context. One option is to use the phrase "specific months," which implies a clear and exact timeframe. Another synonym is "particular months," highlighting the importance or significance of those specific months. "Designated months" suggests that these months have been chosen or assigned for a specific purpose. "Selected months" could also be used to denote a deliberate choice or preference. "Seasonal months" is another option, emphasizing the relationship between the time of year and the relevant months. Overall, using different synonyms can add variety to writing and convey slight differences in meaning.