IPA: /ɪnˈtɛnsɪst/
KK: /ɪnˈtɛnsɪst/
The highest degree of strength or force; the most extreme level of something.
The storm was at its intensest, causing widespread damage.
Comparative: more intense
Superlative: most intense
Intensest is formed from "intense" (from Latin "intensus", meaning stretched or strained) and the superlative suffix "-est" (meaning most). The word "intensest" refers to the highest degree of intensity or strength.
Think of something that is 'stretched' or 'strained' to the highest level — that's what intensest means.