Whisky derives its name from the Gaelic term uisge beatha (pronounced ooshky-bay), which translates as water of life. It has been progressively anglicized over the years from uiskie to whiskie and finally whisky in 1746. Until relatively recently this has been a more unofficial terminology however as early written references to the spirit used the Latin for water of life, aqua vitae. The first known reference famously dates to 1494 with an instruction given by King James IV to Friar John Cor 'to make aqua vitae VIII bolls of malt'.
Malt remains the key ingredient for whisky to this day, referring to cereal grain that is either malted or unmalted. Whilst any cereal grain can be used to make whisky such as corn or wheat, it is barley that must be used to make single malt Scotch whisky. The other permitted ingredients for Scotch whisky are yeast, water and caramel colouring.
Early recipes for whisky would also have included the addition of honey, herbs and spices post-distillation to tame what may have been an unaged and fiery spirit. The term for a spirit flavoured with such things as mace, cloves, cubebs, liquorice and cinnamon has traditionally been usque baugh, separating it from uisge beatha. Dr Johnson's Dictionary of 1755 defined usque baugh as being 'a compound distilled spirit, being drawn on aromaticks; and the Irish sort is particularly distinguished for its pleasant, mild flavour. The Highland sort is somewhat hotter , and by corruption they call it whisky'.
Certainly by the 1750's the term whisky was used with reference to a pure spirit. Later in the belief that unmatured whisky made you fully drunk the 1915 Immature Spirits Act required that to use the term whisky the spirit must have spent at least two years in a cask prior to bottling. Increased to three years in 1916 this law still stands today and anything of a younger age must be referred to simply as spirit or new make spirit.
Today Scotch whisky by law must be matured in oak casks not exceeding 700 litres in an excise warehouse in Scotland. The unique properties of oak add desirable flavours to the spirit whilst also helping to remove undesirable ones. It is the influence of the oak cask that is the biggest contributor to flavour within the finished whisky.