An oilcan is a small metal can for oil, with a long thin tube so you can pour a little oil exactly where you need it — a bicycle chain, a door hinge, a machine. The long nose is the whole point: you are aiming, not dumping. Older ones are often red, with a thumb lever that gives a small squirt. You will meet the word in workshops and in older books more than in a supermarket. Today many people write oil can as two words, or they use a plastic bottle with a thin spout, but the picture in the word is still that metal can with the long nose.