Synonyms for Let down:

n.

divulge, give someone to understand (that), relay, deliver, report, let someone know, brief, advise, tell, point out. mend, take in, stitch, let out, tack, pin up, embroider, alter, turn up, sew. hold back, plague, embarrass, throttle, burden, bring up against, disadvantage, inhibit, count against. miss, trip-up, fall short, mess up, blunder, slip up, err, stumble, foul up. wear down, discourage, cast a shadow over something, dash someone's hopes, throw/pour cold water on something. fall, plummet, drop, plunge, come down, slip, descend, go down, lose your balance/footing. dwarf, scale back, condense, compact, constrict, shrivel, shrink, thin. let down (noun)
disappoint, bring down, get down, lower, take down.

v.

disappoint (verb)
abandon, take down, lower, disillusion, fail, fall short.

Other synonyms:

err, count against, wear down, embarrass, trip-up, scale back, disillusion, disadvantage, bring up against, stumble. fail, foul up, constrict, blunder, discourage, mess up, inhibit, slip up. hold back, condense, throttle. plague, burden, shrivel. shrink. dwarf. compact. miss. thin. humble
take down.
lower
lower.
Other relevant words:
embarrass, throttle, disillusion, abandon, drop, fall short, fail, hold back.