The word itself is a compound one, made from UN + DITH, meaning NOT + SEEN.
Examples of DITHA from GURBANI is
dithaa sabh sansaar sukh na naam bin.
I have seen the whole world - without the Lord's Name, there is no peace at all.
DEKH KE UNDITH KEETA means "Though they had seen, yet they ignored that"
The eloboration of the literal meanings is desired.