落後

to fall behind / to lag (in technology etc) / backward / to retrogress

to leave out / to be missing / to leave behind or forget to bring / to lag or fall behind

colloquial reading for 落[luo4] in certain compounds

to fall or drop / (of the sun) to set / (of a tide) to go out / to lower / to decline or sink / to lag or fall behind / to fall onto / to rest with / to get or receive / to write down / whereabouts / settlement

back / behind / rear / afterwards / after / later / post-

modesty leads to progress, arrogance makes you fall behind (quote of Mao Zedong)

economically backward

a blade will get rusty if it is not sharpened; a man will fall behind if he doesn't study (idiom)