I thought I'd made it up but apparently it's already a (rare) girls' name. (nooo! panic!) Nobody I know has heard of it btw...
Its meaning is defined in Webster's 1913 dictionary as 'evening' and it's also supposed to mean 'evening star' (an old fashioned name for Venus) and there are a few ships used to be named it as well.
I thought it was dignified and beautiful, would have used it for a girl or a boy - but as a middle name, which we are really stuck for, would you think it respectable enough for DS? DS1 has already got used to the two names together, so have I and can't think of anything else...
Name is Hesper. (First name William)