(figurative) a course of action that is unproductive and offers no hope of improvement; "all the clues led the police into blind alleys"; "so far every road that we've been down has turned out to be a blind alley"
the occurrence of incoming water (between a low tide and the following high tide); "a tide in the affairs of men which, taken at the flood, leads on to fortune" -Shakespeare
absolutely required and not to be used up or sacrificed
absolutely necessary; vitally necessary; "essential tools and materials"; "funds essential to the completion of the project"; "an indispensable worker"
being or relating to or containing the essence of a plant etc; "essential oil"
make (alcohol) unfit for drinking without impairing usefulness for other purposes
modify (as a native protein) especially by heat, acid, alkali, or ultraviolet radiation so that all of the original properties are removed or diminished
add nonfissionable material to (fissionable material) so as to make unsuitable for use in an atomic bomb