strengthy
/ˈstrɛŋ(k)θi/Chiefly Scottish and northern in early use
adjective
1Of God, a person, the spirit, etc.: capable of effective action or resistance; mighty, powerful; mentally strong. Now rare ( literary ).
2Physically strong; having muscular strength; robust; able to exert or resist force.
3Difficult to deal with, overcome, or refute; reliable, certain, convincing. Now US informal.
Origin
Late Middle English; earliest use found in The Wycliffite Bible (early version). From strength + -y.