bái tóu xié lǎo
(idiom) (of a married couple) to live together until old age; to remain lifelong companions
白
bái
white
头
tóu
head
偕
xié
in company with
老
lǎo
prefix used before the surname of a person or a numeral indicating the order of birth of the children in a family or to indicate affection or familiarity