This is the result of preposition מִן being attached to the head of תוֹךְ.
Maybe this word appears as an entry in your dictionary and maybe not.
It is more common to find this word under entry תָּוֶךְ, centre, middle, inside: look at ptr N-t113.A.
Now, תּוֹךְ is the (singular) construct: ptr N-t004.A.3.
Strictly speaking this is ptr N-t141.2.
We thus get from (the) midst of, out of