The Collaborative International Dictionary
Toughen \Tough"en\, v. i. & t. [imp. & p. p. Toughened; p. pr. & vb. n. Toughening.] To grow or make tough, or tougher.
Wiktionary
n. The process of making something tougher. vb. (present participle of toughen English)
Usage examples of "toughening".
A warm sensation crawled over my naked balls, elongating and toughening my never-flagging organ.
Her own sex became a taut sheath against his organ, her clitoris toughening, exploding.
And that particular toughening process which had been working on him for years now aided in his speedy adaptation to a new set of facts, formidable ones.
Wearily, Shann spread out his hands in the very faint light of their tiny fire, poked with a finger tip at smarting points which would have been blisters had those hands not known toughening in the past.