IPA: /æmˈbʌʃmənt/
KK: /æmˈbʌʃmənt/
A surprise attack from a hidden position.
The soldiers set up an ambushment to surprise the enemy.
Ambushment is formed from "ambush" (from Old French *embuschier*, meaning to lie in wait) and the suffix "-ment" (meaning the action or result of). The word refers to the act or result of lying in wait to attack unexpectedly.
Think of someone lying in wait ('ambush') for an unexpected attack, and the '-ment' indicates the action or result of that waiting.