66 entries under sound topic. ×

14
obligatory(adjective, certain, true, significant)
13
necessary(adjective, essential, inexorable, required)
8
compulsory(adjective, certain, true, significant)
7
valid(adjective, right, reasonable, severe)
6
stringent(adjective, reasonable, severe, rational)
5
legal(adjective, reasonable, rational)
4
authoritative(adjective, reasonable, rational, unconditional)
4
cogent(reasonable, rational)
4
compelling(verb, adjective, reasonable, severe)
4
good(reasonable, rational)
2
conclusive(adjective, set, reasonable, rational)
2
just(reasonable, rational)
2
lawful(reasonable, rational)
2
legitimate(reasonable, rational)
2
logical(reasonable, rational)
2
official(reasonable, rational)
2
solid(reasonable, rational)
2
substantial(reasonable, rational)
2
ultimate(reasonable, rational)
2
weighty(reasonable, rational)
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APASmart Define. (2015). binding thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/binding/thesaurus/synonyms
ChicagoSmart Define. 2015. "binding thesaurus" https://smartdefine.org/binding/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2015, binding thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/binding/thesaurus/synonyms>.
MLASmart Define. "binding thesaurus" 10 April 2015. Web. 21 September 2026. <https://smartdefine.org/binding/thesaurus/synonyms>