As nouns the difference between memo and second
is that memo
is memo while second
is one that is number two in a series or second
can be the si unit of time, defined as the duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of caesium-133 in a ground state at a temperature of absolute zero and at rest; one-sixtieth of a minute or second
can be one who supports another in a contest or combat, such as a dueller's assistant.
As an adjective second is
number-two; following after the first one with nothing between them the ordinal number corresponding to the cardinal number two.
As an adverb second is
(with superlative) at the second rank.
As a verb second is
(uk) to transfer temporarily to alternative employment.