Using
GUSTS - 2
GUSTY - 2
QUOTH - 2
GULCH - 2
JUNTA - 2
MUSIC - 2
GUSTS, GUSTY, GULCH
If GU??? then
QUOTH => GUO??
JUNTA => GUO?A
MUSIC => GUOIA - Not a word
GUSTS, GUSTY
If G?S?? then
QUOTH, GULCH => G?S?H
JUNTA =/=
GUSTS, GUSTY
If G??T? then
QUOTH, GULCH => G??TH
JUNTA => G?NTH
MUSIC =/=
GUSTS, GUSTY, MUSIC
If ?US?? then
QUOTH => QUS?? or ?US?H
GULCH => QUSC? or ?USCH
JUNTA => QUSCA or JUSCH - not words
GUSTS, GUSTY, QUOTH, JUNTA
If ?U?T? then
GULCH => ?ULT?
MUSIC => MULT? or ?ULTC
GUSTS, GUSTY
If ??ST? then
QUOTH, GULCH => ??STH
JUNTA => J?STH
MUSIC =/=
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best I can come up with is MULTI but that isn't a word by itself.