(of a face) showing no emotion

expressionless

(of a person) not favouring a particular side, opinion etc (in a quarrel)

unfeeling, impartial

(of a person) showing no sign of feeling

aloof, cool

not influenced by personal feelings; not referring to any particular person

cold, unfriendly

that cannot be understood or known

hidden, mysterious; blank

supporting neither side in an agreement or quarrel; belonging to a country that supports no side in a war; having no definite characteristics, colour etc

impartial, noncommittal

not able to oppose the effect of a disease, chemical etc

lifeless, inactive

showing no enthusiasm, interest etc; not willing to fight when attacked or opposed

lifeless, inactive