inexpressive
Word family (noun) expression expressiveness (adjective) expressive ≠ inexpressive expressionless inexpressible (verb) express (adverb) expressively expressionlessly inexpressibly
From Longman Dictionary of Contemporary Englishinexpressivein‧ex‧press‧ive /ˌɪnɪkˈspresɪv◂/ adjective EMOTIONALa face that is inexpressive shows no emotion