The correct spelling of the word "in securest" is actually "insecurest", with stress on the second syllable. It is pronounced as /ɪnsɪ'kjʊrəst/ and is the superlative form of the adjective "insecure". This word is commonly used to describe a state of feeling unsure, uncertain or unsafe. Although the phonetic transcription might seem complicated, it is important to have a clear understanding of the correct spelling and pronunciation of words to avoid confusion and miscommunication.
The word "insecurest" does not seem to exist in standard English.