1
to go out of use;to become obsolete;to die out;to go out of fashion;to go out of style
その風習はすたれつつある。
That custom is on the decrease.
2
to decline (e.g. of morals);to be lost;to go into decline (of a town, business, etc.)
Other forms
頽れる 【すたれる】 (rarely used kanji form)