This is the 3479th most frequent Japanese word.
着い
"着い" is not a standard standalone word in Japanese. It might be a conjugation or part of "着く," which means "to arrive."
The word '着いた' is used here as the past tense form of '着く', meaning 'to arrive'. It indicates the completion of the action of arriving at a location.
駅に着いたら電話してください。
Please call me when you arrive at the station.
In this sentence, '着く' is used in the future tense to describe the occurrence of arriving at a location in the future.
その列車は遅れて着くでしょう。
That train will likely arrive late.
The word '着いて' is the te-form of '着く', which is often used to connect actions or indicate a sequence of events in a narrative around arriving.