Green’s Dictionary of Slang

1. very severe, excessive.

1809

J.W. Croker Croker Papers I (1884) 20: I am [...] completely in office, up to my eyes in business, the extent of which is quite terrific.

2. a general term of approval, wonderful, very good indeed, ‘great’.

1891		Albert Chevalier ‘The Dotty Poet’ 🎵 All his notions are terrific, And I’ll own he is prolific, But he is about as dotty as can be!
1930		D. Mackail Young Livingstones 271: ‘Thanks awfully,’ said Rex. ‘That’ll be ripping.’ ‘Fine!’ said Derek Yardley. ‘Great! Terrific!’.
1942		W.R. Burnett Quick Brown Fox 102: ‘It’s terrific,’ said Joe. ‘Got everything, that story. Color, romance, action, plenty of shooting’.
1955		W. White ‘Wayne University Sl.’ AS XXX:4 302: terrific [...] adj. Terms denoting that somebody or something is good.
1960		Wodehouse Jeeves in the Offing 106: He’s terrific, isn’t he?
1970		T. Southern Blue Movie (1974) 14: Boris nodded. ‘Terrific,’ he said, almost inaudibly.
1981		J. Sullivan ‘Go West Young Man’ Only Fools and Horses [TV script] Yeah, you do that, it’s triffic, great, yeah.
1984		Smiley Culture ‘Cockney Translation’ 🎵 Cockney say t’riffic. We say waaacked!