To denote words ending with -th, I use an *T.

Here are some briefs:

bath= BA*T
beneath= BAO*ENT or NAOE*TH
bequeath= QAO*ET
berth= B*ERT
billionth= B_LT
birth= B*IRT
births= B*IRTS
birthed= B*IRTD
Bluetooth= BL*UT or BLAO*T
tooth= TAO*TH
booth= BAO*TH
both= BO*T or BO*ET
breadth= BRED/*T or BRA*ED
breath= BR*ET
broth= BRO*T
cheth= KH*ET
cloth= KLO*T
cometh= KO*MT
couth= KO*UT or KAO*UT
cruth= KRAO*UT