The most common and most likely answer to this crossword clue is the 8 letter word FLATBILL
I've seen this crossword clue in The Guardian
F
L
A
T
B
I
L
L
Buddy explains!
The straight part
We know that "flycatcher" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flycatcher = flatbill.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FLATBILL mean?
FLATBILL noun- Any of various tropical primarily olive-green flycatchers, having a wide flat bill, members of the genera Ramphotrigon, Rhynchocyclus, or Platyrinchus.