Neologism derived from the root √LA "no, not". ló- and lenition before consonants. It's meant to be used as an alternative to ú-, which Tolkien rejected as a negative prefix in his later writings.
*ló-hevin mass "I do not have bread."
*law aníron mass "I do not want bread."
lā > lǭ > lau, law
?law > ló-