IPA: /ˌɪn.sɪnˈsɪr.li/
KK: /ɪnˈsɪn.sɪr.li/
In a way that is not genuine or truthful; expressing feelings or thoughts that are not sincere.
She apologized insincerely, making it clear she didn't really mean it.
Insincerely → It is formed from "in-" (meaning not) and "sincere" (from Latin "sincerus", meaning pure or genuine) and the suffix "-ly" (meaning in a manner of). The word "insincerely" means in a manner that is not genuine or pure, often referring to a lack of honesty in expression.
Think of 'not' ('in-') being combined with 'genuine' ('sincere') to remember that 'insincerely' means expressing something that is not genuine.