Green’s Dictionary of Slang

1. to arrive.

1884		Sporting Times 29 Nov. 1/4: He didn’t seem a little bit pleased when she weighed in with a pair of second-hand skates.
1925		Wodehouse Carry on, Jeeves 204: When I got there on the following night, I found I was the last to weigh in.
1926		J. Black You Can’t Win (2000) 115: We parted at Pocatello, agreeing to ‘weigh in’ (meet) at Ogden in the spring.
1933		Illus. Police News 16 Nov. 4/4: ‘Weigh in at 10.30 sharp then’ replied the coroner.
1979		J. Morrow Confessions of Proinsias O’Toole 101: Punchy, that bastard, hadn’t weighed in at all on Monday.

2. (US) to assert oneself.

1885		Daily News Nov. in Ware (1909) 260/2: The journal ‘weighs in’ with a prismatic Christmas number.
1909		J. Ware Passing Eng. of the Victorian Era.
1937		P. Cheyney Dames Don’t Care (1960) 117: Paulette weighs in an’ tells him that unless he cashes in she is goin’ to blow what he has been doin’ to the cops.
1941		Baker Popular Dict. Aus. Sl.

3. to pay or give one’s share.

1882		Sporting Gaz. (London) 21 Jan. 65/3: [E]normous crowds, too many of whom their delicate sense of honour does not allow to ‘tip up,’ or in other words, if I may be allowed to use racing slang, will not ‘weigh in’.
1898		Binstead & Wells Pink ’Un and Pelican 257: The sympathetic fair weighed in enough to bury him in the cemetery at Greenwood instead of in the Potter’s Field.
1914		‘Ian Hay’ Lighter Side of School Life 203: Aunt Deborah hasn’t weighed in yet.
1934		Wodehouse Right Ho, Jeeves 69: Anatole […] is always willing and ready to weigh in with some good old simple English fare.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 11: Weigh in: To pay.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xliii 11/2: weigh in: To pay a debt or pay a share.
1975		Bulletin (Sydney) 26 Apr. 44: One of the old rorters up the Cross tugged me coat a week ago. His mail was that if I didn’t weigh in soon I’d be gathered for sure, but, shit, I didn’t expect I’d get dished up like this just on a lousy dud.
1986		R.G. Barrett Godson 258: ‘You blokes have had me round here nearly every day, and I haven’t weighed in a zac’.
1989		(con. 1950s–60s) in G. Tremlett Little Legs 55: You just have to give the police a good talking to, and weigh them in a little bit here and there.
1992		R.G. Barrett White Shoes 3: Price did weigh in the $50,000.
2000		J.J. Connolly Layer Cake 110: They each weigh him in at about twelve gee each.
2002		R.G. Barrett Mystery Bay Blues 19: [He] ran up a fair phone bill [...] When the time came for him to leave, and in a bit of a hurry, he couldn’t weigh in.
2013		T. Peacock More You Bet 7: A person partially settling, or effectively settling a debt, might have been said to have ‘weighed in’ with some or all of the money owed, respectively; and the same term might have been heard in reference to someone making a comment, which was usually an unwelcome or inappropriate comment, which was typically expressed in a sentence such as, ‘And then so-and-so weighed in with such and such’.

4. to join in, esp. in an argument.

1901		‘Hugh McHugh’ Down the Line 37: Buck Jones caromed over from the other end of the car and weighed-in with us.
1945		N. Marsh Died in the Wool (1963) 60: Flossie had always said the Japs would weigh in on our side when war time.
1969		P. Boyle All Looks Yellow to the Jaundiced Eye 77: Properly roused by now, I weighed into her.
1979		F. Norman Too Many Crooks Spoil the Caper 95: Glenys weighed in furiously with her high-heeled shoe clouting the pair of them.
2013		see sense 2.

5. to play one’s part.

1903		Wodehouse ‘How Pillingshot Scored’ in Captain May 🌐 There are some muffins in the cupboard. You might weigh in with them.
1914		Bulletin (Sydney) 27 Aug. 11/1: I can dash off this sort of thing with the utmost readiness, so if there’s any market for it let me know, and I will weigh in with as much as you are able to stand, week by week.
1915		Wodehouse Psmith Journalist (1993) 191: Comrade Windsor knows certain stout fellows, reporters on other papers, who will be delighted to weigh in with stuff for a moderate fee.
1993		D. Jarman diary 22 Apr. Smiling in Slow Motion (2000) 335: I weighed in and completed both canvases by five.