from
The Collaborative International Dictionary of English v.0.48
Pocket veto \Pocket veto\
The retention by the President of the United States of a bill
unsigned so that it does not become a law, in virtue of the
following constitutional provision (--Const. Art. I., sec. 7,
cl. 2): "If any bill shall not be returned by the President
within ten days (Sundays excepted) after it shall have been
presented to him, the same shall be a law, in like manner as
if he had signed it, unless the Congress by their adjournment
prevent its return, in which case it shall not be a law."
Also, an analogous retention of a bill by a State governor.
[Webster 1913 Suppl.]