Green’s Dictionary of Slang

lightweight adj.

(US) insignificant, unimpressive.

1809		E.S. Barrett Setting Sun I 39: May we not see in them the handwriting on the wall, the ‘MENE, MENE, TEKEL, UPHARSIN,’ the end of the government of light-weight princes .
1885		A. Edwardes Girton Girl III 205: I never looked for such a scene — I am not good at these high passions! [...] In everything I am a light weight.
1902		Ade Girl Proposition 3–4: Among the other Things she wore that Evening was a featherweight Escort who had Percy written all over him.
1952		Lait & Mortimer USA Confidential 228: But Milwauke, the lightweight busher, screamed.
1967		M. Braly On the Yard (2002) 344: Cat was just one more lightweight joint wheel, hiding behind a pair of twenty-two inch arms.
1974		V.E. Smith Jones Men 7: Compared to Joe’s [wake] this thing ain’t nothing. This lightweight.
1984		D. Jenkins Life Its Ownself (1985) 44: Fuck you, Kenneth, and everything your lightweight ass stands for.
1997		E. Little Another Day in Paradise 80: These guys are like neo-Nazi lightweight hoods, fucking maroons.
2000		Guardian Rev. 1 Jan. 14: It feels a bit lightweight to be leaving at 4am.
2018		W. Kramer Hard Stuff 45: Gerry and the Pacemakers and Billy J. Kramer and the Dakotas were lightweight.

In phrases

light weight and way late (adj.)

(US black) fashionable, sophisticated.

1938

‘Idioms of the Present-Day American Negro’ in AS XIII:4 Dec. 314/2: LIGHT WEIGHT AND WAY LATE. Same as mellow back.