a person or thing having the same function or characteristics as another
"After moving to London, Sarah quickly found her counterpart in marketing at the local branch who understood the regional sales targets perfectly."
a duplicate copy
"The old machine produced a faded counterpart of the original document that was almost identical in every detail."
Either of two parts that fit together, or complement one another.
"The puzzle pieces clicked into place perfectly because each was the exact counterpart to its neighbor."
Counterbalance.
"The heavy concrete foundation was designed to act as a counterpart to the massive steel crane, preventing the entire structure from tipping over."