The most common and most likely answer to this crossword clue is the 3 plus 4 letter word ERL KING
I've seen this crossword clue in The Guardian
E
R
L
K
I
N
G
Buddy explains!

The straight part
We know that "Bearded giant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bearded giant = erl king.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 ERL KING mean?
ERL KING noun- In German literature and modern pseudo-mythology, a malicious elf or spirit who preys on children.