The Collaborative International Dictionary of English v.0.48:
Inexpressive \In`ex*press"ive\, a. 1. Inexpressible. [R.] [1913 Webster] 2. Without expression or meaning; not expressive; dull; unintelligent; as, an inexpressive countenance. [1913 Webster]WordNet (r) 3.0 (2006):
inexpressive adj 1: not expressive; "an inexpressive face"