From *ga- + *kraftīgōn. *gakraftīgōn to strengthen, empower *gakraftugōn Old English: gecræftgian Old High German: gikreftigōn Middle High German: gekreftigen...
(“powerful, strong”) + *-ōn. *kraftīgōn to strengthen, empower *kraftugōn *gakraftīgōn *kraftīgjan Old English: cræftgian Old Frisian: kreftigia, kreftegia...