The Barnhart Dictionary of Etymology -
Originally from the French ambre (amber) possibly initially derived from the Arabic 'anbar (ambergris). The original meaning of the word amber was ambergris. The modern word is derived from the French ambre gris (gray amber, ambergris) in distinction to ambre jaune (Prussian amber, yellow amber or true amber). The English and French confusion over the terms may have arisen early since both raw substances are relatively similar in appearance, with the exception of color, are rare, are costly and are found on or along seacoasts.
Oxford English Dictionary -
From the French ambre gris (gray amber, ambergris). To this substance the word amber originally referred. Spelling variants may owe their origins to confused attempts to describe the substance as greasy in feel or as coming from Greece or to associate it with amber (yellow amber), itself.
Reported variants are:
Also related are:
Random House Dictionary of the English Language -
Derived from the French ambre gris (gray amber). The word amber originally meant ambergris and was initially derived from the Arabic word 'anbar (ambergris) but was confused with true amber which is also rare, is also found along coasts and may be similar in appearance.
Roget's Thesaurus -