∙ Someone (or something) with thick skin. It is used for animals such as an elephant or a hippopotamus.
∙ A member of the obsolete taxonomic order Pachydermata, grouping of thick-skinned, hoofed animals such as the rhinoceros, hippopotamus, elephant, pig and horse. obsolete, zoology
∙ An elephant informal
∙ A person that is not affected by (does not care about) what others say about him or her. idiomatic