SPINACH
abbigal
cabinetcaboosedebtorsrebuiltonboardmobsterreboundsubsidywebsitetabletssubwayslobsterreboundrebateslibraryrabbitsdebrieffibbingembraceembargolabeledorbitedrebirth
amoebas
There isn't one. You can make the 5 letter word bound
bunting
bathtub, brewpub
Some seven letter words starting with B are:bathtubdisturbperturbproverbrhubarbsuccumbtaxicabwashtub
cobbler
There is no 7-letter word using those letters, but there are two 6-letter options:confabforbad
cribbed
besides
brought