read
dear
rade*
Edar
dare
ader *

* ader wax n. A waxy mineral that is a mixture of hydrocarbons and occurs in association with petroleum; some varieties are used in making ceresin and candles;

* Rade \Rade\ (r[=a]d), n.
A raid. [Scot.]
[1913 Webster]

16? That would mean 4 words starting with D, 4 with E, 4 with A and 4 with R , if you would consider the word 'read'?
I've got six. Impossible task it seems.
Although I'm not good at what seems like mathematics to me, I'm interested.