Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
niggling is an adjective meaning "(informal) small and of little importance". It carries one recorded sense.
(informal) small and of little importance
“a fiddling sum of money”
“a footling gesture”
“our worries are lilliputian compared with those of countries that are at war”
“a little (or small) matter”
“a dispute over niggling details”
“limited to petty enterprises”
“piffling efforts”
“giving a police officer a free meal may be against the law, but it seems to be a picayune infraction”
colloquialism
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 niggling come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.