least aggressive opening

The cow

Now that is conceptually interesting. I guess it all depends on what one means by "aggressive". In one sense, that of not seeking to simply assume the initiative or get into a set of forcing moves, I nominate Basman's "Creepy-Crawly" opening system (sometimes referred to as the "de Klerk"): 1. a3, 2. h3 and move 3 depends flexibly on what Black has done. 3. e3 or 3. c4 or 3. b4 or even 3. g4 come into contention. The idea is to out-finesse the opponent structurally then whack out tactics after the tension gets unbearable.

Thank you

Non-Aggressive Openings often lose or draw!

You often need to be aggressive 1 way or another to win a chess game.

Unless, Your trying to Draw with the Black side pieces?

Thats not a bad idea, but it be tough trying to stick with a non-aggressive approach if your opponent playing white doesn’t cooperate!

In my opinion, I consider aggressive and attacking to be synonyms.

However, it is important to note that aggressive and tactical is not the same thing.

But to answer your question, regardless on how you define the terms the two openings that comes to mind is either London or the English.