Green’s Dictionary of Slang

monty n.

also full monty, monte
[ety. unknown; the success of the 1997 film The Full Monty hugely popularized the phr. and the variety of etys. for monty/monte were proposed, although none has been accepted as authoritative; they range from monte, a Sp. and US Hisp. game of chance, played with a pack of 45 cards, the tailor’s Montague Burton, i.e. a full three-piece suit; the ‘full English breakfast’ purportedly enjoyed by Field Marshall Montgomery, during WWII; the gambling town of Monte Carlo, in which the full monte would equate with ‘breaking the bank’ and several more]

1. everything, all that there is, ‘the lot’; esp. in phr. the full monty.

2. see monte n.1 (2)

3. see monte n.1 (3)