tacit

adj. communicated wordlessly, implied without being expressed in words

The concept of tacit knowing comes from scientist and philosopher Michael Polanyi. It is important to understand that he wrote about a process (hence tacit knowing) and not a form of . However, his phrase has been taken up to name a form of knowledge that is apparently wholly or partly inexplicable.
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Adjective
1. indicated by necessary connotation though not expressed directly; "gave silent consent"; "a tacit agreement"; "the understood provisos of a custody agreement"
(synonym) implied, silent, understood
(similar) implicit, inexplicit

(a.)
Done or made in silence; implied, but not expressed; silent; as, tacit consent is consent by silence, or by not interposing an objection.
  

unspoken but understood.