You came up with the answer to one question . And evaded the others .
The single answer only highlighted the problem of omission , which seems to be catching .
As Circumspice points out , why did you omit "Conventionally, a henge comprises of a a ditch with an external bank with one or more entranceways." ?
Did you also fail to see "Cotton Henge is formed purely of two ditches which would originally have had associated external banks, it never contained any standing stones." too ?
"A henge is a prehistoric monument consisting of a circle of stone or wooden uprights, with Stonehenge in Wiltshire one of the best-known examples." ,
is nearly correct ,all that is missing is the qualifier "sometimes" .
As you have been told many times "Henges are sometimes associated with megaliths but only a very small percentage . "
All the henges that do not have stone or timber circles prove the need for that qualifier .
One of your definitions “Henge = a large stone or wooden post set in astronomical alignment.“.
Note, even by the bbc version , which is hardly ideal , no mention of astronomy ,and the timber or megaliths were in the plural , never mind unnecessary .
Making your definition ,wrong . But we didn't need any more confirmation , we knew that anyway .