'irregularly-used' is a compound formed from 'irregularly' and 'used.' 'Irregularly' comes from 'irregular,' which originates from Latin 'irregularis,' where 'in-' meant 'not' and 'regularis' meant 'regular.' 'Used' is the past participle of 'use,' which comes from Latin 'uti,' meaning 'to use.'

'Irregularly' developed from Middle English 'irreguler' and Latin 'irregularis,' while 'used' comes from Old French 'user' and Latin 'uti.' The compound 'irregularly-used' is a modern English formation.

Initially, 'irregularly' meant 'not regular,' and 'used' meant 'employed or utilized.' Together, 'irregularly-used' means 'not used regularly.'