A googolplex #= 10^(10^100)# is probably the largest finite number with a simple dictionary name.
Explanation:
Names have been proposed for #10^(10^(10^100))#, #10^(10^(10^(10^100)))# and generalisations, namely "googolplexplex", "googolplexplexplex", etc., but they have not been taken up by the major dictionaries.