swinging!, excl. — Green’s Dictionary of Slang

swinging! excl.

[swing v. (9); the term migrated to UK as the catchphrase of entertainer Norman Vaughan, compere of television’s Sunday Night at the London Palladium, who alternated the positive swinging with the negative dodgy; it was further associated with the image of ‘swinging London’ and the ‘swinging Sixties’]

(orig. US black) a general term of approval.

1963

M. Braly Shake Him Till He Rattles (1964) 123: ‘How’d it go?’ she asked [...] he burst out, ‘Swinging! The best jazz crowd I’ve seen.’.