1
to restrict;to limit;to confine
金持ちが必ずしも幸福とは限らない。
The rich are not always happy.
2
to be restricted to;to be limited to;to be confined to
3
to be best (for);to be the best plan;to be the only way (to)
as ...は...に限る
暑い日は冷たいビールに限る。
There is nothing like cold beer on a hot day.