noun / verb
dose
DOHS/dəʊs/
A measured amount given or received at one time.
The marked cup holds a measured dose of medicine.

Etymology
Greek dosis meant “a giving” and was used for a prescribed portion of medicine. That medical use underlies a dose as a measured amount, later extended to other substances.
In context
Scorpions can control the amount of venom they inject, often delivering a smaller dose for defense and a larger dose for subduing prey.