resistant

Short definition from Wiktionary

Noun

1. 1
   A person who resists; especially a member of a resistance movement.
2. 2
   A thing which resists.

Adjective

1. 1
   Which makes resistance or offers opposition.
2. 2
   Which is not affected or overcome by a disease, drug, chemical or atmospheric agent, extreme of temperature, etc.
3. 3
   Not greatly influenced by individual members of a sample.