Subscribe to The Chicago Manual of Style Online
Q. Is it OK to greet someone with “Morning!” or is it “’Morning!”? I’d think that it’s common understanding that you’re saying “Good morning” and not just shouting the time of day at someone.
A. An apostrophe means that letters are missing from a word, not that a word is missing from a phrase. Since “Good morning” is a two-word phrase, there is no reason to use an apostrophe in front of “Morning.” I agree that the phrase is easy to understand in its short form. In a context where it could be confused with shouting the time of day at someone (I like your way of putting it), it would be better to include “Good.”