What does the expression if you catch my drift mean? Where does it originate? I've heard it in the context to signify something like if you know what I mean.
The part "my drift" means there is a chain of thoughts or an inside meaning that is not clearly defined. the expression is used whenever you think the listener may be confused or not follow your main idea.
The origin of the word "drift", according to OED, was in the 1520s:
I can't know for sure the origin of the expression "if you catch my drift".
It means that you have not given a direct answer to a question, or you have not made an explicit statement describing a situation. Rather you have made a statement that should allow a listener / reader to understand what you meant. Essentially, your conversation is drifting towards a statement, but you stop before you get there. You use the phrase to alert the listener that there is an inference to be drawn.
get my drift is another form of this phrase.
if you say:
The phrase has been around a long time. Shakespeare uses my drift (meaning my meaning) a in a few of his plays. The term predates this usage.
Note: the quote is from Real Vampires Have More to Love by Gerry Bartlett.
The phrase means: "If you know where I'm going." (But I don't want to go there.)
Rivers have currents, or "drifts." At places, it's dangerous to go too far along a river.
More to the point, there are often social "currents," that are tricky to navigate. So the speaker doesn't want to go "too far." But if the listener (mentally) "jumps in," where the speaker stops, and follows the "drift" (current) s/he will get the point.