FFF, you were correct just not the best example
An accident occurred when an aircraft was cleared to descend:
ATC: "Descend two four hundred..."
Pilot heard: "descend to four hundred" = CFIT.
(Germany I believe)
Hence we have the word altitude or height in climb/descent clearances.
"Descend to altitude two four hundred" - less ambiguity.
"Descend to altitude two thousand four hundred" - no ambiguity (UK model)
Clearances to FL do not contain the word "to":
"Climb/descend FL40"