Forthwith means immediately and without delay. Cease forthwith, effective forthwith, remove it forthwith.
It is legal and administrative language, and its whole function is to remove any argument about timing — a court order requiring something forthwith means now rather than soon. In ordinary speech it is either deliberately formal or a joke. Note that forthwith is forth plus with, and English kept it while losing most of its neighbours.
1adverbforthwithImmediately and without delay.
“The manager was dismissed forthwith for stealing from the till.”
forthwith is an expression of immediacy.
Middle English forth-with is forth plus with, partly from the phrase forth with something. It is one of a family of forth- compounds that mostly died.
Middle English
forth-with — at once, immediately; at the same time, already; straight ahead
English, today
forthwith
Built from
From Middle English forth-with (“at once, immediately; at the same time, already; straight ahead”)fourth-with, furþ-with, partly from the phrase forth with (something), and partly from forth-with-al, furth-with-al (“at once, immediately; together with”) (whence forthwithal).
Etymology from Wiktionary, CC BY-SA