sentry, century

Sentry or sentry ( sen tree ) means a guard, particularly a guard who keeps unauthorized people out of a restricted area, such as a military base or camp--
They tried to sneak onto the base, but they couldn't get past the sentry.
I can't go. I'm on sentry duty tonight.
He froze when he heard the sentry shout "Halt! Who goes there?"

Century or century ( sen choor ee ) means one hundred ( 100 ) years--
Cars were invented more than a century ago.
In the 19th century, people rode in carriages pulled by horses.

Now that you know that, you can say--
"Even with 21st century technology, the base still needed a sentry at the gate."

Note--a "centurion" was a kind of soldier in Ancient Rome, who commanded a century, meaning 100 other soldiers--
The preacher seemed to refer to the story of the faithful centurion nearly every Sunday.
Note # 2--a bit of trivia--there is a "century plant", a type of agave supposed to flower only once in a hundred years. Not to be confused with  "centaury", an herb that grows in Europe.