The phrase "year in year out" means something that happens consistently or repeatedly, without fail. There are several synonyms for this phrase, including consistently, regularly, routinely, incessantly, perpetually, and persistently. These words all convey the idea of something happening repeatedly over time. For example, someone might say "I work out consistently" to mean they work out regularly, without skipping a day. Or, "I have been walking my dog perpetually for years" to mean they have been walking their dog year in year out. Synonyms are useful for adding variety to your writing and can help avoid repetition.