oil
A water-insoluble organic material which is liquid at room temperature. Vegetable oils are made by living plants. Crude (mineral) oil is a fossil fuel which arose over geological time from the accumulated remains of living things (such as peat on land and plankton on the sea floor).
This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
Read the preface. Order the book.