IPA: /nɒnˈsteɪʃənəri/
KK: /nɑnˈsteɪʃənˌɛri/
Not fixed in one place; able to move or change position.
The nonstationary nature of the object made it difficult to track its movement.
Nonstationary → It is formed from "non-" (meaning not) and "stationary" (from Latin "stationarius", meaning standing or fixed). The word "nonstationary" means not standing still or not fixed in position.
Think of 'not' ('non-') and 'standing still' ('stationary') to remember that 'nonstationary' refers to something that is not fixed in place.