There is an Sanskrit Dictionary online resource at
http://sanskritdictionary.com. It combines several dictionaries such
as Monier Williams, Apte, MacDonell, Vedabase, etc.
There apparently is no corresponding word to suttanta in
Sanskrit, which is a pity because it could help to clarify its
meaning.
It is also not found in BHS . The term sautrāntika, which
is the designation of one of the early Buddhist school, who
accepted only the sūtras
and rejected the Abhidharmais a compound consisting of sautra
+ antika ,''close
to / belonging to the sūtras''.
Perhaps the Pali term suttanta is to be
taken in the same way: i.e. sutta + anta in the sense of
''belonging to / included in the suttas'' as a designation for the
discourses of the Buddha included in the class of literature called
sutta or being a inner part (anta) of the Sutta which
consists of all suttantas?