What is the meaning of the word "gal"?

Definitions:

A casual, friendly way of addressing or referring to a female. NOUN
- I met a gal at the party who shares my passion for hiking.
An abbreviation for gallon, a unit of liquid volume. NOUN
- The tank hold 10 gal of water.
Informal term to refer to a girl or woman. NOUN
- She's a fun-loving gal who always brings positive energy to the room.
Refers to a unit of measurement for acceleration, named after Galileo Galilei, equivalent to 1 centimeter per second squared. ADJECTIVE
- Gravitational anomalies are often expressed in gals, a unit named after the famous scientist.