tough·en 
(tŭfən)
(tŭfən)tr. & intr.v. tough·ened, tough·en·ing, tough·ens
To make or become tough. See Synonyms at harden.
toughen·er n.
- gene therapy
- genetic
- genetical
- genetic algorithm
- genetically
- genetically modified organism
- genetic code
- genetic coding
- genetic counseling
- genetic disorder
- genetic drift
- genetic engineer
- genetic engineering
- genetic fingerprint
- geneticist
- genetic load
- genetic map
- genetic marker
- genetics
- genetic screening
- Geneva
- Geneva
- Geneva bands
- Geneva Convention
- Geneva cross