regress - definition and synonyms

verb [intransitive] 

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/rɪˈɡres/
present tense
I/you/we/theyregress
he/she/itregresses
present participleregressing
past tenseregressed
past participleregressed
  1. to return to a previous and usually less developed state or condition

    Tommy’s speech seems to have regressed since he changed schools.