Definition of henceforth adverb from the Oxford Advanced Learner's Dictionary

 

henceforth

 adverb
adverb
BrE BrE//ˌhensˈfɔːθ//
 
; NAmE NAmE//ˌhensˈfɔːrθ//
 
(also henceforward
BrE BrE//ˌhensˈfɔːwəd//
 
; NAmE NAmE//ˌhensˈfɔːrwərd//
 
)
(formal)
 
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starting from a particular time and at all times in the future Friday 31 July 1925 henceforth became known as ‘Red Friday’. Henceforth, all staff will need to provide proof of identity before entering the building.
See the Oxford Advanced American Dictionary entry: henceforth