This is the 430th most frequent Icelandic word.
seinni
"Seinni" means "later" or "the latter" in English.
In this sentence, 'seinni' indicates the order (the second in a sequence).
Seinni bíllinn er blár.
The second car is blue.
Here, 'seinni' is used to mean 'later' in terms of time.
Ég kem seinni, ekki bíða eftir mér.
I will come later, don't wait for me.
In this case, 'seinni' refers to the later part in a division (the latter half).