Where does the word “spliff” come from?

Neither the OED and Etymonline has any answer to the etymology of the word. The latter does suggest it may have an origin in the Caribbean, but offers nothing better.

The first citation is from 1936 only. Here are the last two citations:

• 1975 High Times Dec. 137/1 — Like Marley, he’s a spliff-toking Rastafarian.
• 1977 Transatlantic Rev. lx. 192 — Coon rolled a massive splif and blew clouds of ganja gremlins through the hatch.

What’s the origin of the word spliff? Might there be precursor that makes sense only if you know the various creoles of the West Indies, or even just the Rastafarian culture?

This unsubstantiated source suggests that spliff is a portmanteau word derived from combining the word split with the word spiff:

(From split <divided> + spiff <well-dresssed or good>)

A quality cigarette rolled with both tobacco and marajuana, initially popular on Europe's Iberian Peninsula.

Additionally, the term has been adopted to mean any high quality or well-rolled marijuana joint.

You can find other citations of the same ilk, but they ultimately trace back to the same origin, which needs further references to be fully satisfactory.

The habit of mixing tobacco with cannabis products (in both leaf form and hashish) is surely an old one, and the Etymonline-suggested alleged origin of the West Indies would be an area where both would freely flourish. So perhaps to them a cannabis cigarette was “spiffier” than a (purely) tobacco one.

Further research will be needed to determine the linguisto-fumatory habits of Jamaican children before the Second World War, given the OED’s very first citation of:

• 1936 Daily Gleaner (Kingston, Jamaica) 3 Oct. 35 - Here is the hot-bed of ganja smoking..and even the children may be seen at times taking what is better known as their ‘spliff’.