The most common and most likely answer to this crossword clue is the 5 letter word OHM’S
I've seen this crossword clue in The Guardian
O
H
M
â
€
™
S
Buddy explains!
The straight part
We know that "law" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case law = ohm’s.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 OHM’S mean?
OHM’S noun- In the International System of Units, the derived unit of electrical resistance; the electrical resistance of a device across which a potential difference of one volt causes a current of one ampere. Symbol: Ω