Weed n.weed; A plant that is unwanted, esp. intrusive, unattractive, or noxious.
So out in the back forty and the front 36.5 we have weeds. Now we do get after the little buggers but apparently they are growing the whole time we are working or watching Gilligan's Island or basting tasty meats. At the moment we are up in the battle, due to some Preem preemergent in the back garden. Yet the lawn on close inspection is at least 10% non-grass plants, the front yard had some nasty blackberry taking over right by the street, and the little yard at the end of the house is threatening to burst again as soon as we avert our eyes.
Now, we use that Roundup stuff that kills everything. At least that is what they breathlessly tell you on the bottle, "...wash off IMMEDIATELY is accidentially sprayed on desired plants...". Our experience is that you have to really hose the suckers down, and double strength at that. We tried an Ortho product that is supposed to kill ivy and kudzu; HA! hardly scared most of what we sprayed. I think aliens must be coming down at night and feeding and watering.
What really works is ripping them out by the roots, after you half kill them with chemicals. That or fire.