Vigor
Vigour, Virility
When you are sturdy and healthy you are full of vigor and virility.
ごうけん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
彼は剛健な昔の武士のような見た目だが、彼の足にある血豆を誤って押してしまった時に、泣き叫んでいました。
He looks like a strong warrior of long ago, but he wailed when I accidentally pressed a blister on his foot.