plumb

Adjective

Positive plumb

Comparative none

Superlative none

1. truly vertical

   if an endlessly long line was plumb, then it would go through the center of the Earth

Adverb

Positive plumb

Comparative none

Superlative none

1. in a truly vertical direction

   same as the adjective meaning

Noun

Singular plumb

Plural none

1. a heavy piece of lead attached to string used to tell whether a line is truly vertical