What does this brainteaser wordplay mean?

[bnorris10]

I need help with this brain teaser please



DOG
THE



What does this mean?


An example of a similar brainteaser is

ablueoncemoon

~Answer~ once in a blue moon

 

[turbo]

How about "the underdog"

 

[bnorris10]

you know that was my first guess just figured it was to easy

 

[DaveC426913]

My favourite has always been:

S ... D COUSIN


(second cousin, once removed)