downbeat vs let-down

downbeat

• Cautiously optimistic. 

• Sad or pessimistic. 

• The accented beat at the beginning of a bar (indicated by a conductor with a downward stroke). 

let-down

• A disappointment or anticlimax. 

• The clearance of an aircraft to descend through clouds to clear air below, or the process of granting such a clearance. 

• The neurohormonal release of milk in dairy cows or in breastfeeding human mothers.