牢固性的英文：
fastness ;firmness

fastness是什么意思：
n. 要塞,巩固,迅速

This is a fast delivery.
这是一个快投球。

You cannot react fast enough to just be a fast follower.
只做一个快速跟进者不能保证反应得足够快。

He runs as fast as Paul.
他跑得和保罗一样快。

Run as fast as you can.
你能跑多快就跑多快。

Why, I was fast asleep.
怎么，我睡得很熟的呀。

firmness是什么意思：
n. 坚固；坚度；坚定

Are the firm's finances sound?
这家公司的财务状况可靠吗?

His step was not as sharp and firm.
他的脚步不再像从前那样敏捷、坚实。

To become firm or gelatinous; congeal.
凝固凝结或变硬；冻结

To make or become firm.
使稳定，使变坚固

make firm or secure; strengthen.
使坚固或安全；强化。