Left in, to a proofreader

• Didn't take out
• Marked text to keep
• Decided to keep
• Kept in
• Horse keeping dry, put back as before
• Nullified a deletion
• Marked for inclusion
• Changed one's mind, in printing

Wiktionary Word definitions in Wiktionary
vb. (en-past of: stet )

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Stet \Stet\, v. t. [imp. & p. p. Stetted ; p. pr. & vb. n. Stetting .] (Print.) To cause or direct to remain after having been marked for omission; to mark with the word stet, or with a series of dots below or beside the matter; as, the proof reader stetted ...