If you do something beforehand, you do it earlier than a particular event.
例句
How could she tell beforehand that I was going to go out?...她怎么會事先知道我要出去？Saunas can be hazardous if misused. Avoid a big meal beforehand.洗桑拿浴如果方法不當會有危險，浴前切忌飽食。
英漢詞典釋義
adv.
預先, 事先
Please inform me of your arrival time beforehand.請事先通知我你抵達的時間。
英英詞典釋義
Adjective
1. being ahead of time or need;
"gave advance warning""was beforehand with her report"
Adverb
1. ahead of time; in anticipation;
"when you pay ahead (or in advance) you receive a discount""We like to plan ahead""should have made reservations beforehand"