Full Idea
An 'enthymeme' is a deductive argument with an unstated assumption that must be true for the premises to lead to the conclusion.
Gist of Idea
An 'enthymeme' is an argument with an indispensable unstated assumption
Source
Stephen Yablo (Aboutness [2014], 11.1)
Book Reference
Yablo,Stephen: 'Aboutness' [Princeton 2014], p.179