You can think of dinky as one size smaller than you expected. The smallness is the first thing you notice, and it is not good or bad on its own. What decides the feeling is your reaction to it: the size can look just right and charming, or it can look like not enough. British speakers usually lean the first way, American speakers usually lean the second, which is how one short word ends up carrying two opposite tones.
From the word’s history
Wiktionary dates dinky to about 1780-90 and compares Scots dink, meaning neatly dressed or trim, plus the ending -y. It gives the possible path as trim, then dainty, then small, then insignificant. That path lines up with the two adjective senses we have: British English stopped at the dainty stop, American English went on to the insignificant one.
維基詞典把 dinky 追到大約 1780-90 年，並拿蘇格蘭方言的 dink（穿得整齊、俐落）來比對，後面加上 -y。它給的路線是：整齊 → 精緻小巧 → 小 → 微不足道。這條路線剛好對上我們手上的兩個形容詞意思：英式停在「精緻小巧」那一站，美式走到了「微不足道」那一站。維基詞典自己用的是「可能」，所以這條線索當參考就好。
Wiktionary, "dinky" (etymology 1)
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