Every now and then when I'm reading, even though I think I'm getting the meaning of specific military terms from the context, I'll find one or two I just have to look up.
The two most recent ones were "invest" (as in "their forces then invested the town") and "saw off" (as in "the Prussian cavalry then saw off the Austrian attackers").
Both are terms I'd heard before, and was pretty sure I understood the meaning, but both were quite interesting to look up.
In the case of "invested" I always took it to mean "laid siege to" or, more accurately "surrounded". I was happy to learn that "surrounded" or "encircled" is probably closest to the meaning. I wasn't sure if it simply meant "encircled" without indicating a formal siege, but I'm pretty sure it can mean just that, "surrounded" as opposed to "attempted to breach the walls". Etymology says: from Latin investire "to clothe in, cover, surround," but also gives "besiege" as a meaning. I always took "besiege" to be more active, and "invest" to be more in the line of "surrounded". I now see that "besiege" is fairly passive as well, as it simply means to "sit down" before a fortress or city, and not necessarily to attempt to breach the walls.
In the case of "saw off", I assumed it meant something like it does when you walk a guest to the door, or drive your friend to the airport, that is, "made sure they were on their way". I didn't realize that "see off" also has two other meanings, which are more in a military context, viz, "to make someone go away or leave a place, especially by chasing them" and "to deal successfully with someone or something, especially by defeating them easily".
Interesting what you find when you actually take the time to verify your assumptions.
How about you?
Any somewhat vague terms that you just had to look up, to really verify the meaning?