Grammatical term for words like "yesterday", "today", "tomorrow" [duplicate]
It depends on the usage. "Yesterday," "today," and "tomorrow" can either be nouns or adverbs. In "Today is a good day." Then "today" is a noun. But if you say, "I'll see you tomorrow," then it's an adverb, since "tomorrow" is modifying the verb, "see." If it's an adverb, it's sometimes called an adverb of time, along with other words like "later," "now," "next year," or "last week."