The Collaborative International Dictionary of English v.0.48:

Observantine \Ob`ser*van"tine\, n. [Fr. observantin.] (R. C.
   Ch.)
   One of a branch of the Order of Franciscans, who profess to
   adhere more strictly than the Conventuals to the intention of
   the founder, especially as to poverty; -- called also
   Observants.
   [1913 Webster]