Etymology From gi(ga)- + -illion. Modelled after million, billion etc. Compare also jillion.
1
UK, Rare A thousand million, proposed as an alternative to the (now little used) British milliard and the (ambiguous, in the UK) US billion.
The internationally agreed symbol for 10^6 is M and this is the initial letter of million. Would it not be logical and convenient to turn this happy accident into a principle and use G, the internationally agreed symbol for 10^9, as the initial letter of the word for 1,000,000,000? That number would thus be called a gillion. Whether the g should be hard or soft is a matter of opinion. I incline to hard because of the derivation from giga.1968, N. W. Pirie, More About the Units (Nature vol. 220):
gillion
noun
Etymology From gi(ga)- + -illion. Modelled after million, billion etc. Compare also jillion.
At Guy's school there had been an outdoor pool, in use from April to October, a watery grave for a billion insects, or quite possibly a gillion or a squillion. The bright turquoise lining had wrinkled under the children's feet.2012, Rebecca Smith, A Bit of Earth:
I looked down to see my dog, Roof, short for Rufus, curled in sleep below the window, unworried by the wings of hummingbirds whirring at speeds of a gillion miles an hour as they flitted in and out of the trumpets of honeysuckle growing on the side of the house.2022, Frank Voss, My House Was Not a Home: