Looks like a specialty bottle top possible a medicine bottle. Thats a pour spout for maybe cough syrup or some other liquid. The bottles cap wound have screwed down over the spout it looks like. Maybe it also used a cork stopper.....
I'm pretty sure I've seen those before. I've been collecting bottles for over 20 years, but mostly poison and some apothecary. This is modern, as in early 1900's (well, modern as far as antique bottles are concerned) and is a molded bottle, not a BIMAL bottle. It used a screw cap, not a cork as the opening isn't perfectly round. This is a lamp oil bottle, most likely from the 10's or 20's. The notch allowed you to line up the bottle while filling the lamp correctly so that the non-round spout allowed it to "burp" while pouring without shooting oil everywhere.
That is definitely a lamp oil bottle. You can see that the seam of the bottle travels from the bottom all the way to the lip so it's definitely molded. I would date it most likely post 20's since it has a plastic cap. Plastic wasn't invented until 1907 and wasn't really widely used for bottles until the 20's. Really cool find though. I'm guessing, given the purpose, these are pretty common, however since I don't collect oil bottles I'm not sure. I don't see any mold marks on the bottom which is another mass production clue. There was most likely a few producers of these that resold them to companies that filled and labeled them, otherwise there would be mold marks on the bottom. I'm guessing this is either a 20oz bottle or a "#20" aka "size 20."
Also, just in case people are curious and don't want to google "BIMAL" it means "Blown In Mold Applied Lip." The glassmaker would blow the glass into a 2 piece mold giving it a seam up to the middle or so of the neck. Then, a separately molded lip would be molded onto the previously blown bottle.