annealing Definition

to heat and then cool (a material, such as steel or glass) usually for softening and making less brittle; also : to cool slowly usually in a furnace

to cause two complementary strands of nucleic acid (such as DNA or RNA) to join by hydrogen bonding; also : to induce the binding of a genetic primer to a complementary single-stranded nucleic acid by slowly cooling single strands obtained from the heating and separation of double-stranded DNA or RNA

strengthen, toughen