IPA: /ɪnˈsoʊʃəbl/
KK: /ɪnˈsoʊʃəbl/
Not inclined to seek the company of others; unfriendly or reserved.
He was often seen as insociable because he preferred to spend time alone rather than with friends.
Insociable → It is formed from "in-" (meaning not) and "sociable" (from Latin "sociabilis", meaning able to be associated with others). The word "insociable" means not able to be associated with others or not inclined to socialize.
Think of 'not' ('in-') being combined with 'able to socialize' ('sociable') — that's why insociable means not inclined to socialize.