day one(redirected from since day one)
The first day or the beginning of something. Honestly, I've loved Frank since day one, long before we officially started dating. I'm sorry, but your assistant has annoyed me from day one! How can you stand her constant cheerfulness?
the very beginning; the very first day. (*Typically: from ~; since ~.) You haven't done anything right since day one! You're fired! She was unhappy with her new car from day one.
n. the first day. (Often with since.) You haven’t done anything right since day one! You’re fired!