a missile equipped with a device that is attracted toward some kind of emission (heat or light or sound or radio waves)
"The anti-aircraft gunner adjusted his aim as the seeker locked onto the heat signature of our stealth bomber."
One who seeks.
"The young seeker refused to join the established congregation, believing that only a direct revelation from God could validate true faith."
A member of an English Protestant dissenting group that emerged around the 1620s; they considered organised churches to be corrupt and preferred to wait for God's revelation.
In plain English: A seeker is someone who actively looks for something they want, like answers or a new experience.
"The seeker was determined to find the lost key in the pile of leaves."
The word seeker comes from Middle English, formed by adding the suffix -er to the verb seek. It entered modern usage with its current meaning of someone who searches for something.