having similarity in size, shape, and relative position of corresponding parts
"The butterfly's wings are perfectly symmetric, displaying an identical pattern on both sides where each vein corresponds to its partner across the center line."
Symmetrical.
"The butterfly's wings are perfectly symmetric, mirroring each other on either side of its body."
The word symmetric comes from the noun symmetry and the suffix -ic. It traces its roots back to the Latin term symmetria, which itself was borrowed from the Ancient Greek summetría.