This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
冸 combines the ice radical 冫 with 半, but the exact historical development is uncertain. It may have originally related to melting ice, given the kun reading と.ける, but this is speculative.
The ice radical 冫 beside 半 suggests something about ice or cold, but without a clear meaning, picture a half-frozen block of ice that is starting to melt.
For ハン, imagine a half-melted ice cube in your hand: hand -> ハン, and the ice is slowly melting.