...The last sentence would justify the coining of 'answerful', for comic effect.
One thing to be aware of is that the suffix doesn't always have the same meaning. A 'hopeful' person may be said to be
full of
hope (but even here I have my doubts, as the 'fullness' is only for one thing - not a general optimism); but a useful knife isn't
full of
use - unless it's a
http://en.wikipedia.org/wiki/Swiss_Army_knife: and a fretful baby is not
full of
fret (which isn't even a noun, nowadays - although in some dialects people still use the expression 'in a fret' to mean 'disturbed')... And as for a wistful or baleful glance, all bets are off! ;-)
Similarly, a motherless child has
no mother; but a fruitless exercise has nothing to do with fruit; a wireless router doesn't have
no wires (the connections it can make don't
use wires, which is not the same) ....
b
PS Informally, 'needful' can be used to mean 'that which is needed' - it doesn't mean 'full of need', for which there is the word 'needy'. This usage seems to me to be dying out, but older people may still talk about 'doing the needful'.