Functional group Ethers

[Hector_Galarza_2E]

If asked to identify the functional groups in a molecule, would ethers be considered a functional group or a substituent? I am confused on what to call it because when naming molecules they are treated as substituents but yet are labeled as a functional group why?

[Chem_Mod]

Ethers are simply unique in terms of naming molecules but they are still functional groups.