经年累月
jīng​nián​lěi​yuè

for years

  1. 经 經 jīng verbpreposition
    to pass through
    to pass through; to undergo; to experience
  2. 年 nián noun
    year
    a year or the duration of a year; also used to describe annual or yearly occurrences
  3. 累 lěi verbnoun
    to accumulate
    (bound form) to pile up; to accumulate; to build up
  4. 月 yuè noun
    month
    month; a time unit based on the cycle of the moon, twelve of which make a year; also used for monthly occurrences or payments