every preparation possible; all aspects of preparation
Emphasizes that preparations are thorough and complete, leaving nothing undone. Often used in formal or written contexts.
I made every possible preparation for the trip.
All preparations for the meeting are complete.
Similar meaning, but 準備万端 is more common and slightly less formal. 用意万端 is a rarer variant.
Compound of 用意 (preparation) and 万端 (all matters, everything). The exact historical derivation is uncertain, but the combination naturally yields the meaning 'every preparation possible'.