uncharacteristic
UK: ˌʌn.kær.ək.təˈrɪs.tɪk | US: ˌʌn.ker.ək.təˈrɪs.tɪk
Definition
adj. not typical or usual for a particular person, thing, or situation
Structure
un <not>character <distinctive quality>istic <adjective suffix>
Etymology
The word combines:
- "un-" (Old English "un-," meaning "not"), a common negating prefix.
 - "character" (from Greek "kharaktēr," meaning "engraved mark" or "distinctive quality"), which evolved to signify individuality.
 - "-istic" (from Latin "-isticus," via Greek "-istikos"), forming adjectives meaning "pertaining to."
The fusion reflects a logical progression: "not" + "distinctive quality" + "pertaining to" = "not typical." 
Examples
His uncharacteristic silence during the meeting surprised everyone.
The sunny weather was uncharacteristic for November.
She made an uncharacteristic mistake in her presentation.
The dog's uncharacteristic aggression worried its owner.
Such uncharacteristic behavior might indicate stress.