"Meet up with an old friend" 可以用英文表达为 "catch up with an old friend"。
其中 "catch up" 是一个短语动词，意思是 "赶上，追上"。在这里，它的意思是追上失去联系的老朋友。
举例来说：
I'm going to catch up with an old friend tonight.
(我今晚要和一个老朋友见面)
I haven't seen her in ages, I'm really looking forward to catching up.
(我已经很久没见她了，我真的很期待能和她见面)
也可以用"meet"来表示这个意思
I'm going to meet an old friend tonight.
I haven't seen her in ages, I'm really looking forward to meeting her.