- the middle of a stream or river（溪或河）中流：
the ferry was moving out into midstream.
渡船开始驶向中流。
- Medicine (of urine) passed in the middle part of an act of urinating【医】（小便）排至一半的。
短语
in midstream
1
- in the middle of a stream or river在中流。
1.1
- figurative (of an activity or process, especially one that is interrupted) part-way through its course〈喻〉（尤指被中断的活动、过程）中途的; 半途的：
our conversation was interrupted in midstream.
我们谈到一半时被打断了。