What does the cryptic crossword clue "Small flier then, or cuckoo (6)" mean?

The definition is "Small flier". The wordplay uses an anagram. anagram of THEN, + OR = HORNET; definition: "Small flier" The answer is Hornet.

Small flier then, or cuckoo (6)

Telegraph Prize Cryptic #3007 | 19 Across | 2019-06-09 flower