FOM: definitions

[Thomas Forster]

Does anybody know anything worthwhile written on the theory
of definitions since: Suppes - intro to logic?  I read this when
it came out and it was one of the things that persuaded me that
logic really mattered.  I now have a student who wants to work
on it.  Annoyingly, he picked up Martha Kneale's copy in a
second-hand bookshop and - even more annoyingly - won't sell it
to me.  
     But never mind about that - anybody got any hot tips about
good stuff to read since 1957?

              Thomas Forster