1. To allow something to remain in a lowered position. A noun or pronoun can be used between "leave" and "down." We're leaving the windows down to help clear some of the smoke out of the kitchen. I like the idea of a convertible, but I would never leave the top down because I hate having all that wind blowing around me while I drive.
2. To go without taking someone or something from a lower position, place, or level. A noun or pronoun can be used between "leave" and "down." I left the kids down in the play room while I went up to have a shower. I think I left my phone down in the kitchen.
3. To cause one to be at a lower financial level than before. A noun or pronoun can be used between "leave" and "down." The market failure of our latest product left us down by about $2.5 million for the quarter. Another projected dip in the market is expected to leave investors down as much as 4.5 per cent.
4. To allow oneself to become lapsed or complacent in one's caution, vigilance, or preparedness. A noun or pronoun can be used between "leave" and "down." The enemy camp leaves its defenses for one hour each night at 3 AM—that's when we will strike! There will always be people in this business looking to exploit you, so you can never leave your guard down.
leave something down
to leave something in a lowered or low position. Leave the window down, please. It's hot in this car. Leave the window down. This house is cold enough as it is.