乍 zhà means: suddenly; for the first time; newly; abruptly. It often appears in these three formulas to mean at the first sight/glance/listen/thought, etc.
Formulas of 乍
1. 乍 + 一 + verb, for example, 乍一看/瞧/听/想/见, etc
分别多年，乍一见我都不认识你了。After so many years of separation, I could hardly recognize you when I first saw you again.
合同中可指两件或两件以上事，但乍一看似乎并不具有误导性的词。Words in a contract which can mean two or more things, but which do not appear to be misleading at first sight.
乍一想, 这一计划还相当实用。At first thought, the plan was quite practical.
现代音乐乍听起来可能让人很不舒服。Modern music can at first seem displeasing to the ear.
2. 乍 + verb +上去
奇怪的是他这个人乍看上去还挺有意思，这方面大家都有同感。The strange thing was that at first sight he looked most interesting. Everybody agreed about that.
乍看上去，他不像个医生。 At first glance, he doesn’t look like a doctor.
乍一听，觉得很荒唐。At first listen，it sounded ridiculous.
3. 乍 + verb + 起来
Modern music can at first seem displeasing to the ear. 现代音乐乍听起来可能让人很不舒服.
At first appearance, the boy seemed very bashful. 乍看起来，这个男孩似乎很腼腆。