RhymeZone: let-down definitions

Definitions of let-down:

noun: (countable) A disappointment or anticlimax.
noun: (countable, uncountable) The neurohormonal release of milk in dairy cows or in breastfeeding human mothers.
noun: (aviation) The clearance of an aircraft to descend through clouds to clear air below, or the process of granting such a clearance.

(Definitions from Wiktionary)