The word 措手不及 is formed by the sequential combination of the characters 措 (to arrange or handle), 手 (hand), 不 (not), and 及 (to reach). The first two characters, 措手, create a verb-object phrase meaning "to take action with one's hands", while the last two, 不及, form a resultative complement meaning "not in time". When combined, the entire phrase literally expresses the idea of being unable to put one's hands to work in time, which conveys the meaning of being caught off guard or unprepared.