Strange act; it is unspoken (5)
I believe the answer is:
tacit
'unspoken' is the definition.
(I've seen this in another clue)
'strange act it' is the wordplay.
'strange' indicates an anagram.
'act' with letters rearranged gives 'tac'.
'tac'+'it'='TACIT'
'is' acts as a link.
(Other definitions for tacit that I've seen before include "Silently understood" , "Unrecorded" , "Unspoken but implied" , "Wordless" , "Implied but not directly expressed" .)