The IUPAC name of $\mathrm{CH}{}_3\mathrm{CH}{}_2-\mathrm{O}-\mathrm{CH}(\mathrm{CH}{}_3)-\mathrm{CH}{}_2-\mathrm{CH}{}_3$ is:

The ether is named by alkoxy prefix on the larger alkyl group as the parent. The larger group is the four-carbon butyl chain attached through carbon 2, and the smaller is ethoxy. The name is 2-ethoxybutane (3-ethoxybutane would use the wrong end).