Late Middle English (in the sense 'give a share of'): from Old French impartir, from Latin impartire, from in- 'in' + pars, part- 'part'.

• part from Old English:

  This is from Latin pars, part- ‘part’, the same Latin source that gave us depart (Middle English); particle (Late Middle English); particular (Late Middle English) ‘small part’ with the sense ‘attentive to detail’ developing E17th; participate ‘take part in’ (early 16th century); partisan (mid 16th century) ‘one who takes the part of’; partition (Late Middle English) ‘something that divides into parts’; and party (Middle English). This last was originally used in the sense of a political party, and only developed the social gathering sense in the early 18th century. Latin a parte ‘at the side’ gives us apart (Late Middle English), and via French, apartment (mid 17th century), while Latin impartare ‘give a share of’ gives us impart (Late Middle English) and impartial (late 16th century).