a-b-a words

$words=WordData[All];

$words//Length

$words[[1]]

$xyxWords=Union@Flatten[StringCases[Flatten[$words],a__~~"-"~~b__~~"-"~~a__]]

$xtoxWords=Union@Flatten[StringCases[Flatten[$words],a__~~"-to-"~~a__]]

mcListToHTMLList[
Map[
"<a href=\"http://www.oxforddictionaries.com/definition/english/"<>#<>"\">"<>#<>"</a>"&,
SortBy[Complement[$xyxWords,$xtoxWords],StringSplit[#,"-"][[2]]&]
]
]