gistfile1.txt

---
- hosts: all
  connection: local

  vars:
    role: foo

    descriptions:
      foo: "this is the description for foo"
      bar: "this is the description for bar"

  tasks:

  - debug: var=role

  - debug: msg="{{ descriptions[role] }}"

gistfile2.txt

PLAY [all] ********************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [debug var=role] ********************************************************
ok: [localhost] => {
    "role": "foo"
}

TASK: [debug msg="this is the description for foo"] ***************************
ok: [localhost] => {
    "msg": "this is the description for foo"
}

PLAY RECAP ********************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0