What does it mean to save?

Today’s research lead to a startling conclusion: I don’t know the meaning of the word ‘save.’ The following definitions of the word ‘save’ appear in the Merriam-Webster Dictionary.

Save, sAv, verb.
a. To put aside as a store or reserve: ACCUMULATE (saving money for emergencies)
b. To spend less by (save 25 percent)

I’m on board with the “store or reserve” definition. In fact, until very recently (i.e. this morning), I was convinced that saving money was the opposite of spending money. You know the old saying, “a penny saved is a penny earned”? Well, I believed it.

You can imagine my shock to read the “to spend less by” definition. I thought that advertisers were just being clever when they tell you that you can “save big money” on their products. I’m embarrassed to admit that over the past decade, I have uttered the phrase “you can’t save money at a sale” at least a thousand times.

With all due respect to the dictionary people, I don’t really accept “to spend less” as a meaning for ‘save.’ I mean, let’s be logical, ‘spend’ is the antonym for ‘save’; how did it also manage to weasel its way up to the definition?