Word Usage – How to Use the Latin Word ‘Cum’ in a Sentence

Cum grano salis is the Latin version of the phrase "take it with a grain of salt". This phrase means:

(With) a grain of salt, in modern English, is an idiom which means to view something with skepticism, or to not take it literally.

There is an interesting explanation to it, which says:

Since in Italy "to have salt in your pumpkin" (avere sale in zucca - pumpkin is a humorous way to say "head") means to have intelligence and reasoning capabilities, "grain of salt" often means "a little bit of intelligence". So, "cum grano salis", in its Latin form, it is often used when it is needed to show that intelligence and personal judgment are needed, as in "I drink wine cum grano salis since I must drive" (with care, moderately) or "please, repair this electric cable cum grano salis" (not scanting, thinking to the consequences or dangers of repairing your electric cable).

The phrase "take it with a grain of salt" is a rather common idiom in English. According to this Google NGram, the Latin form was originally more popular but around 1900 the trend switched to favor the English.

Nowadays, I had never heard the Latin phrase until you posted it. The English version seems to have mostly taken over. I think that using the Latin in conversation would lead people to believe that you were deliberately trying to seem learned, which might come off as disingenuous. The blogger you quoted uses the Latin phrase in a few different articles, but unless you're talking to professors or academics I wouldn't use it in conversation.

Your assumption about it's meaning is largely correct. It typically is used to transition from one subject to another subject on the same topic.

It's meaning can also be expanded to include associated emotions or feelings. This can be seen in similar expressions like: "On a happier note" or "On a sad note."