Mid 17th century: from Latin obesus 'having eaten until fat', from ob- 'away, completely' + esus (past participle of edere 'eat').

• eat from Old English:

  For such a fundamental concept, it is unsurprising that eat is an Old English word, with an ancient root shared by Latin edere ‘to eat’. This is the source not only of edible (late 16th century), but also comestible (Late Middle English) ‘something edible’, edacious (early 19th century), a rare word for ‘greedy’, and obese (mid 17th century) from obedere ‘eat completely’. There are many phrases associated with eating. Eat, drink, and be merry, for tomorrow we die is a combination of two Biblical sayings, ‘A man hath no better thing under the sun, than to eat and to drink, and to be merry’ (Ecclesiastes) and ‘Let us eat and drink; for tomorrow we shall die’ (Isaiah). You are what you eat is a proverb that first appeared in English in the 1920s. It is a translation of the German phrase Der Mensch ist, was er isst, ‘Man is what he eats’, which was said by the philosopher Ludwig Feuerbach (1804–72). If you eat your heart out you suffer from excessive longing or grief. As eat your own heart the phrase was first used in Edmund Spenser's The Faerie Queene (1596): ‘He could not rest; but did his stout heart eat.’ See also fret