unmarked

adjective

1. not marked.
2. Linguistics.
   1. characterized by the absence of a distinctive phonological feature, as (p), which, in contrast to (b), lacks the distinctive feature of voicing.
   2. characterized by the absence of a grammatical marker, as the singular in English in contrast to the plural, which is typically marked by an -s ending.
   3. neutral with regard to an element of meaning specified by a semantically related item.
   4. occurring more typically than an alternative form.Compare marked(def 4).

adjective

1. not carrying a mark or marksan unmarked police car
2. not noticed or observed

adj.c.1400, “having been given no mark,” from un- (1) “not” + past participle of mark (v.). Cf. Old Norse umarkaðr. Meaning “not noticed or observed” is recorded from 1530s.