primer

A molecule, often a small polymer, that initiates synthesis of a larger molecule. In molecular biology: DNA polymerase is dependent upon a small oligonucleotides as a primer to initiate replication. These primers are complementary & hydrogen-bonded to a sequence on the DNA strand to be replicated, resulting in a short segment of double-stranded DNA or DNA-RNA in the case of reverse transcriptase.

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999