by Jove!, (an exclamation used to emphasize an accompanying remark or to express surprise, approval, etc.):
It was a good fight, by Jove!
Origin
1325-75;Middle English < LatinJov- (oblique stem of compound nominative Juppiterfather Jove), akin. to deus god; cognate with GreekZeús (genitive Diós) Zeus
Roman god of the bright sky, late 14c., from Latin Iovis, from PIE *dyeu- "to shine," with derivatives referring to the sky, heavens, a god (see diurnal, and cf. Zeus). In classical Latin, the compound Iuppiter replaced Old Latin Iovis as the god's name.
Idioms and Phrases with by jove
by Jove
Also, by cracky. Used to express surprise or emphasis. For example, By Jove, I was glad to see her, or It was a great day, by cracky. These mild oaths are euphemisms, the first for “by Jesus” or “by God” (Jove is another name for Jupiter, the principal Roman god), and the folksy variant by cracky for “by Christ.” Both idioms may be dying out.