One way to hold payback: something goes out from you, and later something comes back along the same line. You pay, and it comes back. The noun names whatever arrives on the return trip, or how long that trip takes. Fill the return trip with money and you get a profit; fill it with the harm someone did to you and you get revenge; measure it with a calendar instead of a sum and you get a period of time.
From the word’s history
Wiktionary records payback as a deverbal noun from the phrasal verb pay back. The two words are still visible inside it: pay, and back.
來源記錄 payback 是從動詞片語 pay back 直接轉成的名詞。pay（付）和 back（回去）這兩塊到現在都還看得見，這也是為什麼它的每個意思都繞著「回去／回來」這條線。
Wiktionary entry 'payback' (packet evidence kaikki:3f6f69a190036ae4:1157180410, etymology_text: 'Deverbal from pay back.')
登入就可以看每一支怎麼連回核心畫面。