yesterday (Noun) — The day immediately before today. ex. "it was in yesterday's newspapers"
yesterday (Noun) — The recent past. ex. "yesterday's solutions are not good enough" ex. "we shared many yesterdays"
yesterday (Adverb) — On the day preceding today. ex. "yesterday the weather was beautiful"
yesterday (Adverb) — In the recent past; only a short time ago. ex. "I was not born yesterday!"