The gill is a unit of volume in the imperial unit system and uses the symbol gi.
It represents 1/4 of a pint - so in this instance, it is 1/4 of an imperial pint - therefore measures exactly 142.0653125 ml. It's also equal to 2 imperial cups and 1/32 of an imperial gallon.
It is pronounced with a "J" sound at the beginning - and it actually part of a humorous in the nursery rhyme 'Jack & Jill'.
In the UK it was used throughout pubs as standard measures; for example spirits were served as 1/6 gill as standard. In Scotland it was 1/5 gill and in Ireland 1/4 gill. It's still used in the Republic of Ireland today.
The US liquid pint is a unit of volume in the US customary system with the symbol pt.
1 US liquid pint is equal to 1/8 US liquid gallon. This is equal to 1/2 US liquid quart, 2 US cups, 4 US gills or 16 US fluid ounces. The SI / metric equivalent is 473.1765 ml.
From the early (1707) adoption of the British wine gallon at 231 in³, the American pint was born. Where all pints are 1/8 of their respective unit system's gallon, that put the US pint at 28.875 in³.