'periodically-applied' is a modern English compound formed from the adverb 'periodically' and the past participle 'applied'. 'Periodically' itself comes from 'periodic' + the adverbial suffix '-ally', and 'applied' is the past participle of 'apply'.

'periodic' derives from Greek 'periodos' (peri- 'around' + hodos 'way, path') via Latin and French into Middle English; 'apply' comes from Latin 'applicare' (from ad- 'to/toward' + plicare 'to fold') and entered English via Old French and Latin-derived forms. The compound 'periodically-applied' is a straightforward modern English combination of these elements.

The component words originally referred separately to 'recurring cycles' and 'bringing into contact or use'; combined in modern usage they mean 'brought into use at regular intervals'.