Diffusion (noun). the act of diffusing, or the state of being diffused; a spreading; extension; dissemination; circulation; dispersion. Diffusion (noun). the act of passing by osmosis through animal membranes, as in the distribution of poisons, gases, etc., through the body.
Learner's definition of EXCITEMENT. 1. [noncount] : a feeling of eager enthusiasm and interest : the state of being excited. Our excitement was building/growing/mounting as the end of the game approached. His hands shook with excitement. The child cried out in excitement.
It means the high point of something. Something builds up in excitement to a point where the excitement is intense, then the excitement subsides. This applies whether the excitement is sexual or the excitement of a movie or story plot.