The Collaborative International Dictionary of English v.0.48:

Oiler \Oil"er\, n.
   1. One who deals in oils.
      [1913 Webster]

   2. One who, or that which, oils.
      [1913 Webster]

   3. An oil tanker.
      [PJC]

   4. A ship which is powered by oil.
      [PJC]

   5. An oilcan.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

oil tanker \oil" tank`er\ n.
   A ship having large compartments, designed to transport crude
   oil over the ocean.
   [PJC]

WordNet (r) 3.0 (2006):

oil tanker
    n 1: a cargo ship designed to carry crude oil in bulk [syn: oil
         tanker, oiler, tanker, tank ship]