In “一网打尽” what does 尽 mean?
Usage

When you see V+盡, it means to complete the action to full extent. (i.e. 盡 is adverbial)

吃盡珍饈百味 To have eaten all kinds of delicacies
費盡心思 To rack one's brains (lit. to have spent thoughts completely)
把賊人一網打盡 To have caught the thieves at one fell swoop

The objects are 珍饈百味, 心思, and 賊人 (fronted).

In classical Chinese, 盡 can act as a verb meaning 'to deplete' or 'to be depleted'. You may find this in modern Chinese through idioms or common collocations (in that case, it would be 盡+N):

一飲而盡 To drain the cup
盡心盡力 To devote one's heart and energy


As an adverb, it is sometimes possible to see 盡+V (its preceding the verb) because classical Chinese does not make the distinction between V+盡 and 盡+V.1

盡如人意 To have something entirely as someone wishes
盡信書不如無書 (lit. Believing everything in books is worse than having no books at all.)



Glyph origin

盡 depicts a right hand brushing an emptied vessel (皿) (see bronze script below), which symbolises the end of eating (of course there is semantic generalisation).

尽 (the simplified character) is the cursive script of 盡 in printed form (see Wen Zhengming's cursive below, and appreciate how the cursive resembles both 盡 and 尽 at the same time). We call this phenomenon 草書楷化. It is one of the methods of character simplification (see the second entry of the Wikipedia section here).




Character





盡



尽






1 蔣紹愚（2004）從“盡 V——V 盡”和“誤 V/錯 V——V 錯” 看述補結構的形成。語言暨語言學，5(3)，559–581。http://www.ling.sinica.edu.tw/Files/LL/Docments/Journals/j2004_3_02_0638.pdf