makeup
penman
pneuma
punkey
unmake
The largest number spelled without any repeating letters is "one thousand." Each letter in this phrase is unique, and it represents a significant value without any duplicates in its spelling. Other large numbers like "eleven" or "hundred" contain repeating letters, making "one thousand" the largest valid option.
hydro-pneumatic ambidextrously
ParticularProclaimed
Walk my dog. :)
juvenalostim
Without repeating, 4. With repeating, 8.
uncopyrightable Dermatoglyphics misconjugatedly
Five thousand. Any higher number of thousands will repeat 'n' and/or 't' and any number higher than 999,999 will repeat 'l' (as in million, billion, trillion, ...).
Jamoriten Jamie-o-ree-tan
Cornelius
There are actually two: dermatoglyphics and uncopyrightable. Also, it is 'without', not 'whithout'.
26 x 25 x 24 = 15600