Somewhat cool; moderately cool in temperature or manner, or somewhat distant in emotional tone.
From 'cool' plus the diminutive/approximative suffix '-ish' (meaning somewhat or rather). This suffix pattern (reddish, bluish, coldish) allows for less extreme descriptors.
The suffix '-ish' is incredibly productive in English—you can add it to almost any adjective to mean 'somewhat' or 'rather,' which is why words like 'coolish,' 'pinkish,' and 'ridiculous-ish' feel instantly understandable even if you've never heard them.
Complete word intelligence in one call. Free tier — 50 lookups/day.