Appendage (noun)

1. A part that is added to something larger.
2. A limb or other body part that is not essential for survival.

Origin:

Late 16th century: from latin appendere "hang on" + -age.

Examples:

1. The tail is an appendage of the spine.
2. The tentacle is an appendage of the octopus.
3. The wings are appendages of the bird's body.
4. The human appendix is a vestigial appendage.
5. The extra rooms added to the house are appendages to the main structure.