'emission-heavy' is a compound word formed from 'emission' and 'heavy'. 'Emission' originates from Latin 'emissionem', meaning 'a sending out'. 'Heavy' comes from Old English 'hefig', meaning 'having weight'.

'Emission' evolved from Latin 'emissionem' through Old French 'émission' to modern English 'emission'. 'Heavy' has remained relatively unchanged from Old English 'hefig'.

Initially, 'emission' referred to the act of sending out, but now it often refers to pollutants released into the environment. 'Heavy' has consistently meant having weight or being substantial.