insecurely has no recorded synonym. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is securely.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
in a tentative and self-conscious manner
“she always acts very insecurely in the presence of her father”
in a manner involving risk
“our positions here at the university are rather insecurely supported by grant money”
Synonyms, antonyms and the broader and narrower relations for insecurely come from Princeton University’s WordNet. Full sources and licences.