The most common and most likely answer to this crossword clue is the 5 letter word MOSES
I've seen this crossword clue in The Times
M
O
S
E
S
More clues leading to the result MOSES
- Prophet’s artistic grandma
- Doctors succeeded saving European national leader
- Grandma’s tips on jam: no additives; sterilise jars
- Prophet Amos esteemed, to some extent
- One who laid down the law: Grandma, possibly?
- Lawmaker takes a stroll, avoiding Yankee
- Some other fractions in the end found by relative, 1/100
- Liberator frees fifty as from thick treacle
- He led an exodus from Spain through boggy ground
- Natural lining material wrapped round end of the contents of basket
Buddy explains!

The straight part
We know that "One who laid down the law" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who laid down the law = moses.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.