英和和英

It happened to me only once.

one state at a time

for this once

the state of being one

the condition of happening or existing only once during a person's lifetime

only that thing

one's situation of being alone

having only one spouse at a time

producing only one offspring at a time

a one-off, the state of not being a series

He is a monomaniac.

an act of setting one's heart on only one thing

the action of doing something by oneself

a state of appearing on the surface to possess a quality that does not exist at a deeper level

exclusive devotion to the interests of something

a mature and independent person who is a full-fledged member of society

the act of mixing something together as one thing