Due means expected at a certain time, or owed. The train is due, rent is due, due respect.
The two senses are one idea: what is due is what is owed, whether that is money or an arrival. Due to means caused by, and its use to mean because of has been argued about for a century and lost. Due north means exactly north. Note that the word comes from the Latin for owing, like debt.
1adjectivedueExpected at a certain time.
“The next bus is due in ten minutes.”
2adjectiveowedOwed as a payment or right.
“She finally received the money that was due to her.”
Too few real examples of this word to estimate which sense is commonest.
due is a state of being owed or expected.
Old French deu is the past participle of devoir, to owe, from Latin debere. Debt and duty come from the same owing.
Proto-Indo-European
*gʰeh₁bʰ-
Latin
dēbeō — to owe
Old French
deu — due
Middle English
dewe
English, today
due
Built from
From Middle English dewe, dew, due, from Old French deu (“due”), past participle of devoir (“to owe”), from Latin dēbeō (“to owe”), from dē + habeō.
Etymology from Wiktionary, CC BY-SA