persistent and resilient in character or spirit; unyielding

toughness; resilience

firm and indomitable; tenacious and unyielding

soft yet tough and resistant to breaking or snapping

tenacity; resilience; perseverance

possessing great mental or spiritual strength and the ability to withstand hardship

the degree of toughness or flexibility of a material or substance, representing its resistance to being broken or deformed

(botany) bast; phloem