From Old English 'lyft' (weak, worthless) — unusually, English adopted a derogatory term for the left side.
On or toward the side of the body where the heart is located in most people; the opposite of right.
From Middle English 'left, luft,' from the Kentish or East Anglian form of Old English 'lyft-' meaning 'weak, foolish, worthless, idle.' The word replaced the earlier standard Old English term 'winestra' (friendlier, more favorable — itself a euphemism, as in many cultures the left side was considered so unlucky that its true name was avoided). Proto-Germanic *luft- may connect to Middle Dutch 'luft' (left) and East Frisian 'luf' (weak). The left side was considered unlucky, inauspicious, and weak across Indo-European cultures: Latin 'sinister' (left) acquired its English meaning of 'menacing' from this prejudice
Almost every European language uses a euphemism for 'left' rather than calling it what it is. French 'gauche' meant 'clumsy'; Italian 'sinistra' meant 'unfavorable'; Russian 'левый' (levyy) is relatively neutral, but Old English 'winestra' meant 'friendlier.' English is nearly unique in having adopted the bluntly negative 'left' (weak, worthless) as its standard term.