這個拼法底下其實是2個不同的字，意思沒有關係， 只是長得一樣。下面分開列出來。跳到 公基金 · 貓咪
A different word that happens to sound the same. Picture a jar on the table with everyone's coins in it. Each person has put in a share, nobody's share is separate any more, and the pile now belongs to the group. Every meaning on this side is that pile — what changes is only what happens to it at the end.
Wiktionary marks this kitty's origin as uncertain, and only suggests it may be kit ('collection of items') + -y. It is filed under a separate etymology from the cat word, so the two are best treated as different words wearing the same spelling.
Wiktionary 說這個 kitty 的來源不確定，只提出一種可能：kit（一組、一堆東西）加上 -y。它在字典裡被放在跟貓那個 kitty 不同的詞源底下。所以最好把它們當成兩個剛好同形的字，不要硬去牽關係。
Wiktionary (kaikki extract, source_ref kaikki:3f6f69a190036ae4:743653461): “Origin uncertain; etymology 2 sense 2 (relating to card games) is possibly from kit (‘collection of items’) + -y (diminutive suffix).”
One branch
大家湊起來的那一堆
兩個意思共用同一個罐子的畫面，分岔點在結局：一個是大家一起花，一個是贏的人整堆拿走。
noun · B2
Money that a group of people have put together and keep for something they share — office coffee, a class present, a weekend trip. It is spoken of as one pot, 'the kitty', which people put money into and take money out of.
公基金
A second word, same spelling
One picture here: someone crouching down, hand out, voice gone soft, saying the word to an animal that may or may not come. Kitty is cat with the softness left in. It is the word a child reaches for first, the word you use at the door with a dish of food, the word that turns a stray behind the building into somebody's animal.
Wiktionary gives kitt(en) + -y, the little-and-fond suffix that also makes doggy and granny. The softness is built into the ending, which is why the word sounds closer and warmer than cat.
Wiktionary 把它拆成 kitt(en) 加上 -y，那個表示「小小的、疼愛的」字尾，跟 doggy、granny 是同一套。疼愛的感覺其實就藏在字尾裡，所以它聽起來比 cat 近、比 cat 軟。
Wiktionary (kaikki extract, source_ref kaikki:3f6f69a190036ae4:743621199): “From kitt(en) + -y (diminutive suffix). Compare Dutch katje.”