If I said "We have a lunch pending" I would mean we have decided to have a lunch, but have not scheduled the exact time or date yet.
One dictionary says pending also means "forthcoming". That sounds like the good translation for this sentence and but it adds the idea that it is coming soon. These are subtle differences in meaning.
I'm a native american english speaker and "forthcoming" or "upcoming" is the meaning that this sentence implies to me.
The phrasing probably wouldn't be used in a casual setting but I can see it used in a professional one. A usage scenerio might be that someone is asked for something and responds "I'll have to get back to you about that, I have a pending lunch." Meaning a meeting over lunch.
Pending in this case means closer to 'awaiting' or 'waiting for'. A common phrase is 'He was freed pending his trial' which means he is out of jail while waiting for his upcoming trial. I have heard 'We have lunch pending' at business meetings where it means that lunch is ready and waiting for us (typically said when a morning meeting is running late).
I agree. The context of this sentence is absent, so it could mean a lot of things. But if the meaning were that lunch is ready and we should go to the table, then an English speaker would say, we have lunch waiting. To have a lunch pending, would imply a lot of uncertainty. It could be tomorrow, next year, or whatever.
I think we often collocate this word with decision, so we might associate it with something that hasn't been decided yet. But it can be used with other words, too. A pending sale is going to happen, is scheduled to happen, no further decisions about it happening need to be made, but since it is pending, it hasn't happened yet.
I agree, my mom would say "Lunch is waiting" meaning it is on the table. She never said lunch awaits or is pending. Furthermore I haven't heard any of those three -- waiting, awaits, pending -- with a social lunch appointment. Perhaps in some kind of a business setting a lunch appointment might be the critical step we are waiting on and thus could use those words in that context.
I would expect "We have a lunch waiting" if there is a lunch waiting, I would say "We have lunch waiting" meaning the lunch, i.e., the food which was ordered or prepared is sitting at the table and we should go in and sit and eat. When I try to imagine the indefinite article there, (We have A lunch waiting.) I picture a conference where some poor excuse for a lunch is in the next room if you really want it. But in either of these two cases I cannot imagine hearing a lunch is pending.