Somewhat chilly; moderately or slightly cold in temperature or manner; having a somewhat cold or unfriendly quality.
Chill (noun/adjective) + -ish (suffix meaning somewhat or having qualities of); '-ish' is incredibly productive in English for expressing 'sort of' or 'kind of' qualities.
The -ish suffix is pure genius for British English especially—it lets you express vagueness and understatement perfectly, which is why you get words like 'chillish,' 'whitish,' and 'biggish' instead of precise terms.
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