gladh-

verb. to laugh, to laugh [at a joke], *guffaw

This word is not compatible with the name Lalaith “Laughter” attested in The Silmarillion. The most likely explanation of this name is that it is the unattested verb ✱lala- “laugh” with the abstract noun suffix -th seen in tirith “watch(ing)” and sirith “flowing”. This indicates a primitive form ✶lala- instead of ✶glada- (both primitives produce Quenya lala-). If you were to accept gladh- as the Sindarin word for “laugh”, then the word for “laughter” would perhaps be the equivalent abstract noun ✱gladhath, and the name Lalaith might be a mix of Quenya and Sindarin. @@@ Neo-Sindarin uses

gladh-

verb. to laugh

gladha

laugh

(verb) gladha- (i **ladha, in gladhar**)

gladha

laugh

(i ’ladha, in gladhar)

lala-

verb. to laugh

lall

noun. laugh