1The influence of sex on a decision, action, or outcome; sex as a component or property of something.

2Biology. A substance responsible for sex determination or sexual differentiation; specifically a gene or group of genes responsible for sex determination or for the sex-limitation of other genes; (in bacteria) a gene or group of genes (located on either a chromosome or a plasmid) which can promote the transfer of genetic material from a (‘male’) bacterium in which it is present to another (‘female’) in which recombination then takes place.