What does 收 mean in 他把何进部下的兵都收归己有?
收 http://www.cantonese.sheik.co.uk/dictionary/characters/687/
[3] [v] receive; accept; take

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歸 http://www.cantonese.sheik.co.uk/dictionary/characters/2343/
[3] belong to; rest with; be in charge

己= self
有= possession
收歸己有 = &quot;take possession and make it belong to oneself&quot;
There's a common phrase &quot;收歸國有&quot;, which means &quot;Take possession (of a company) and assign it to become State-owned &quot; . Similarly &quot;收歸己有&quot; in your sentence would mean : &quot;&quot;Take possession (of an army) and assign it to become Self-owned &quot;