Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
subnormal is a noun and adjective meaning "a person of less than normal intelligence". It carries 2 recorded senses.
a person of less than normal intelligence
below normal or average
“after the floods the harvests were subnormal”
“subnormal intelligence”
statistics
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for subnormal come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.