Synonyms for belittle

Most common

1. Disparage — to disparage, depreciate, or minimize the importance, value, merit, or significance of someone or something

2. Diminish — to make small

Other

bad-mouth, pick at

v. 1
To disparage, depreciate, or minimize the importance, value, merit, or significance of someone or something.
Don't belittle your colleagues.
v. 2
To make small.

Past participle: belittled
e.g. belittled → disparaged, denigrated, trivialized, downplayed…

Belittle or Disparage?

To disparage is to belittle by damaging comparison or suggestion; it is used only of things.

J. C. Fernald, English Synonyms and Antonyms (1914)

downplay If you try to downplay this, I'm going to walk away.
denigrate Some translate while others denigrate.
disparage We didn't mean to disparage our contenders.
trivialize While I don't want to trivialize your concerns, is all of this really necessary?
minimize I want to minimize the chances of another accident.
diminish This doesn't give him the right to diminish Muslims.

Use in printed books, per decade from 1850 to 2019.

5 letters: lower², abate², decry²
6 letters: reduce², slight¹, shrink¹, lessen²
7 letters: degrade², besmall
8 letters: minimize³, diminish³, minimise, downplay², derogate, smallify
9 letters: disparage³, denigrate³, underrate³, deprecate³, underplay³, dispraise
10 letters: depreciate⁴, understate³, condescend³, trivialize⁴, trivialise
11 letters: subordinate⁴, deemphasise
13 letters: underestimate⁵

The small number after each word is its number of syllables (lower² = 2 syllables).