toughenverb trans and intrans (toughened, toughening)

• perovskite
• peroxide
• peroxy
• perp
• perpendicular
• perpetrate
• perpetual
• perpetual calendar
• perpetual check
• perpetual motion
• perpetuate
• perpetuity
• perplex
• perplexity
• per pro
• perquisite
• perron
• perry
• pers.
• per se
• persecute
• persecution complex
• perseverance
• perseverate
• perseveration