identical, monozygotic (technical)
dizygotic (technical), fraternal, non-identical
conjoined, Siamese
long-lost
His long-lost twin was searching for him.

older, younger
I was the older twin.

female, male
evil
the plot device of giving a character an evil twin

pair, set
a pair of identical twins

be carrying, be pregnant with, expect
give birth to, have
My sister had twins.
He had a twin (= a twin brother or sister).

raise
adult twins who were raised apart

separate
The twins were separated at birth.
an operation to separate conjoined twins

boys, girls
She had twin girls.

daughters, sons
brother, sister

Twin is used with these nouns:
bed, bedroom, brother, city, daughter, engine, goal, sister, spectre, town, track