-eroo Also -aroo, -aroonie, and -eroonie.
An informal and often humorous intensifier of nouns.
[A fanciful formation of uncertain origin.]
This ending is most common in North America, Australia, and New Zealand. It appeared in the US in the 1930s, but its origin is not known. It may be that it was influenced by the older buckaroo, a cowboy, which derives from Spanish vaquero; its acceptance in Australia and New Zealand may have been helped by the model of kangaroo, wallaroo, and other words. It sometimes implies something sizeable, overwhelming, remarkable, or unexpected.
Examples include boozeroo (sometimes boozaroo), New Zealand slang for a drinking spree; jackaroo or jackeroo (from the proper name Jack), a learner or tyro at any occupation, especially a young man working on a sheep or cattle station in Australia to gain experience (the rarer female equivalent is a jillaroo); flopperoo, a complete failure or flop, especially with theatre, cinema, or TV audiences or critics; and smackeroo, in the US variously a hard smack, a kiss, or a sum of money. The extended forms -aroonie and -eroonie (adding the diminutive suffix -ie, see -y2) have been current in the US since the 1960s, for example in smackeroonie.