'power-demanding' is a modern English compound formed from 'power' + the present-participle adjective 'demanding'. 'power' in English ultimately comes via Old French from Latin roots meaning 'ability/force', and 'demanding' derives from the verb 'demand', from Old French 'demander' (to ask/request).

'power' developed in English from Old French 'povoir'/'pouvoir' (a word for ability/force) and Latin roots such as 'posse'/'potis'; 'demand' came into English from Old French 'demander', from Latin 'demandare' ('de-' + 'mandare'). The adjective 'demanding' (literally 'requiring') has been combined in modern usage with nouns like 'power' to form compounds such as 'power-demanding'.

The components originally carried senses of 'ability/force' ('power') and 'to ask/require' ('demand'); combined as 'power-demanding' the phrase specifically came to mean 'requiring a lot of power', a sense that grew with industrial and electrical technology.