名詞 meantime:

1. the time between one event, process, or period and another
   同義詞：interim, meanwhile, lag

副詞 meantime:

1. during the intervening time
   同義詞：meanwhile, in the meantime

1. I like skiing and in the meantime, I know it is very dangerous.
   我喜歡滑雪，同時(shí)也知道這非常危險(xiǎn)。
2. Physicists are studying new ways of generating electricity with less damage to the environment. In the meantime, many power plants are being modernized to give off less polluting material.
   物理學(xué)家們正在研究對(duì)環(huán)境危害少的發(fā)電新方法，與此同時(shí)，許多發(fā)電廠也在實(shí)現(xiàn)現(xiàn)代化以減少污染物質(zhì)的釋放量。
3. You buy the fruits, in the meantime I'll cook breakfast.
   你去買水果，同時(shí)我來做早餐。

mean.time

n.（名詞）
The time between one occurrence and another; an interval.
當(dāng)中時(shí)間：一個(gè)與另一個(gè)出現(xiàn)間的時(shí)間；間隔
adv.（副詞）
During a period of intervening time; meanwhile.
在間隔時(shí)間內(nèi)；與此同時(shí)

Meantime is more common than meanwhile as a noun:
meantime 作為名詞比 meanwhile 更為普遍：
例句：
In the meantime we waited.
我們?cè)谶@時(shí)等待著。

As an adverbmeantime is less common than meanwhile :
作為副詞meantime 不及 meanwhile 普遍：
例句：
Meanwhile we waited.
與此同時(shí)，我們等候著。

All of these uses are standard, however.
但是這些用法都是標(biāo)準(zhǔn)的