Do the letters ol in a substance only indicate that the substance is an alcohol if they came at the end of the name of a substance?
Yes, the ending ol in a name is a good hint that the compound contains an $\ce{OH}$ group.

However, beware of trivial names: 


$\alpha$-tocopherol is not an aliphatic alcohol, but a substituted phenol
mannitol does not contain one $\ce{OH}$ group, but six of them


It's getting even more confusing if you consider other languages, such as German. Benzol is the German name of benzene, which has no $\ce{OH}$ group at all. The same is true for styrol, the German word for styrene ;-)