孜孜不倦

zī zī bù juàn

lit. diligent and never slacking (idiom); continuous concentrated effort

assiduous (in study); to concentrate

孜

zī

used in 孜孜[zi1 zi1]

孜

zī

used in 孜孜[zi1 zi1]

不

bù

no; not so

倦

juàn

old variant of 倦[juan4]