'constantly-used' is a compound word formed from 'constantly' and 'used.' 'Constantly' comes from Latin 'constans,' meaning 'standing firm,' and 'used' is the past participle of 'use,' from Latin 'uti,' meaning 'to use.'

'Constantly' evolved from Old French 'constanter' and Latin 'constans,' while 'used' comes from Old French 'user' and Latin 'uti.' The compound 'constantly-used' is a modern English formation.

Initially, 'constantly' meant 'firm or steadfast,' and 'used' meant 'employed.' Together, 'constantly-used' now means 'employed all the time or very frequently.'